If my credit card was used on Amazon, doesn't that mean someone has my cvv number? And would that mean I have a virus? Or is there another way they can get a CVV code off a credit card? I know it's possible a site stored it when they should NOT have, but that's the only other way I can think of.
Call your credit card company and ask them whether the CVV number was supplied as part of that transaction. (I don't think Amazon has ever asked for mine.)
Even if it was, that doesn't necessarily imply a virus or other malicious software on your computer. That number could have leaked from another merchant, or even from someone to whom you presented your card in person. That said, if you don't have anti-malware software, you should correct that today.