How do i check for viruses?!

I need to know how to check if i have a virus.

Okay, this is what happened: I'm on google. i click on a picture. Of a Lion. I go to the page. And then all of a sudden, the whole web page turns to something that looks like a finder window, except it's still on a Safari browser. There are folders i don't recongnize and one of them says "Trogen" and somehting was suddenly scanning my computer! Then i got a pop up that said "Serveral viruses are on your computer. You need to download virus software" or something like that (i stupidly didn't write the message down because i was freaking out) and it said something about a thing called "Hacktrack" or "hacktrap" (like i said, i didn't write down the exact word.

Anyway. It wouldn't let me leave the page until i said okay to the pop up. I couldn't even shut down the system.

I clicked okay. And nothing happened. I haven't noticed anything yet and i'm running disk utility as i type.

Was this just a joke? Is my computer in danger? Anyway, please give me some advice on what to do. And maybe a like to a virus checker.

Also, if any experts here wants the link to the website i was on, in order to check it out, or ban it, or whatever, let me know.