Sounds like you're having trouble with some machines with minds of their own! ;>)
Are their Mac versions of the anti-spyware software listed above? I am full of questions because we are getting a Mac next week. I use my work laptop now, and it goes through my company intranet first, which has mega-firewalls and security, so I am almost completely pop-up free right now. Don't want to get into trouble with our new Mac!
I don't think you'll need it. I've been using a Mac laptop for 18 months now and have never had a piece of spyware. My Windows desktop is continually infested. BTW, I went to Apple's website support section and searched on the word "spyware" and got no hits. It's just not an issue. You will never regret getting a Mac.