Why have 40+ processes of iexplore.exe been spawned?

"I've seen this behavior on others machines before. I know you've run HijackThis already, but give MBAM (Malwarebytes' Anti-Malware) a try, it may have missed something. A lot of malware will try and ""phone home"" to give the coder information as to what the software is doing, or just as a notification that it's up and running on a remote machine. They may also be using your machine to visit other sites for various reasons (gaining ad revenue, DoS, etc). A lot of coders don't properly terminate these forked processes and this is what you get as a result.

I'd also download Sysinternals TCPView and see what these IE processes are connecting to."