Norton kept blocking the install of TortoiseCVS because it said it was "Suspicious.MH690".
In the end I had to turn off Norton's protection to get it to install.
After I turned NIS back on, it proceeded to wipe the file that ended up in the Norton Recycle Bin after the installer deleted it.
Specifically it was flagging the postinst.exe executable which converts the old settings from an .ini file into registry settings. The source code for the executable is available at the TortoiseCVS sourceforge page and if you look at it you can see that postinst.exe is not a virus.