That sounds familiar. Can't remember the name of the bug, but I do remember not being able to open task manager, and it was masquerading as an antivirus program. I had to use a tool called rkill to interrupt it.
I picked it up from a banner ad as I recall. Even if you trust a site, they can still run ads that will infect your machine. There are ways to protect yourself from this though.
Yes, moderators, I know you're watching. And I know the rules. However, I'd like you to consider this: What do you think it says about those rules, or what it says about you, when I have to choose between following the rules on a forum and providing useful advice to a person on how not to get infected? Don't you think some leeway is in order for this kind of thing? What kind of bastard puts what is convenient for the site ahead of the security of its users? Are you really that much different from Sony, Ubisoft, EA, or any of the other companies whom you ridicule for their disregard for their consumer's security or property?
Anyway, aside from things that I can't mention here, you can switch from Internet Explorer to Firefox if you haven't already, and maybe get the NoScript addon which disables page scripts from running by default. If you don't have an antivirus program, avast is a popular choice.