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I had the same thing happen to me, only the damage was limited to one fraudulent charge on my account.
I saw a popup come up in Firefox with the word 'install' in it, then a command prompt, and both disappeared. Seriously, to the untrained eye, they wouldn't have noticed anything, and if I hadn't been paying attention I wouldn't have caught it. Turns out it was an Iframe exploit. It all happened in a half a second.
I started up both ad-aware and spybot, checked for updates, then disconnected my machine from the internet. In the 2 minutes it took to update spybot and ad-aware, the bot scraped my internet cache and my CC info sent it off to the interwebs. Spybot found the malware, as did Ad-aware. Still, the malware was fast enough.
The very next day I received a call from my CC fraud prevention unit, asking if I'd paid for an AdultFriendFinder sub. Turns out it was flagged as fraud since the charge didn't have my CCV2 number. It either wasn't stored in the internet cache, or I disconnected in time. My cc company is great at handling fraud, and the fraudulent charges were reversed in no time.
I know people clear their internet cache on a regular basis, especially if they're going trolling for *cough* WarezSerialzHax *cough* somewhere like astalavista or the like. Just sayin. If you're going to the dark side of the internet, use protection. Patch the fvck out of your system, and keep your antivirus/spyware solutions updated at all times. if you don't have antivirus/spyware, get the aforementioned three, and AVG free if you're a cheapskate.