API for Determining if App is Running on Citrix or Terminal Services

I'm looking for an API/function I can call to determine if software is running on Citrix, Terminal Services, or a stand-alone PC. Optimally, it would work something like this:

Select Case APIWhatSystem.Type.ToString
   Case "Citrix"
      bCitrix = True
   Case "TS"
      bTerminalServices = True
   Case "PC"
      bPC = True
End Select

I would prefer something that worked from an API call as opposed to looking at something in the registry as we're having more and more customers that are locking down the registry.

Thanks.

Solution

According to: http://forums.citrix.com/message.jspa?messageID=1363711 you can check the SESSIONNAME environment variable.

Another simpler way is to read the system environment variable "SESSIONNAME". If it exists and starts with "ICA" then you're running within a Citrix session. If it starts with "RDP" then you're running within an RDP session.

I tested it with my PC and locally I get:

C:\>echo %SESSIONNAME%
Console

While remotely I got

C:\>echo %SESSIONNAME%
RDP-tcp1

So it seems like it might be an easy route to go, otherwise it sounds like checking for registry values or if certain dlls exist will be the next best thing.