Spysweeper, which is a spyware detector, not an anti-virus program, is detecting the fact that mIRC has scripting capabilities. I'm not 100% familiar with that program, so I'm going to recommend that you:
A) ensure that your spyware definitions are up-to-date (they should be more recent than the release date for mIRC 6.17).
B) rescan your system with the updated definitions and see if mIRC (or any other program) is still being caught.
C) if mIRC is still being detected, go through the settings (might need the help file for Spysweeper also) and locate the area where you can specify programs to be ignored.
D) if you can't find this area, refer to the Spysweeper webpage for assistance.
E) if (worst case scenario that I'm able to think of at this time) Spysweeper does not have an option for that, look into getting a different spyware program (there's lots of them out there)