Read this months (Sept '06)Consumer Reports for a good article on computer security, including product recommendations. It does list my suggestion- Kaspersky- but only as Anti-Virus as the “suite” version I am using is too recent. However, their recommendations are usually excellent.
No, QED if you read the OP, his homepage is being hijacked, thus at the very least he is being infected with a “home page hijacker”.
Possibly. He doesn’t say if he’s tried to change his homepage back. If he has and it keeps going back to securitynetpage.net, then you’re right. It’s also possible that he visited that page (or one of its evil affiliates) and a malicious script changed the homepage that one time. I also missed the extra toolbar he mentions at the end of his post. THAT sounds like some sort of malware, yes. I agree a full spyware sweep is advisable, in any case.
Check out this malware removal thread at SpywareInfo; they are using SmitFraudFix to remove this nasty. While I haven’t run into it personally (yet!), I am filing this away for that eventuality. As the SmitFraudFix tool removes specific files peculiar to the SmitFraud malware, I would say the evidence is pretty damning.