Are you infected by a botnet?
I read with interest about a group of researchers who have managed to (at least temporarily) disable one of the bigger botnets online. I frequently get junk emails from legitimate email addresses that I'm pretty certain are generated by one of the botnets, which often makes me wonder just how many of the people I'm connected to are inadvertently contributing to the problem. Botnets are a little trickier than viruses in that they mostly aren't going after anything specific on your computer. They are largely focused on building an army of zombie computers to make distributed attacks elsewhere. This means your computer could easily get infected and you wouldn't know it because your daily usage won't be impacted directly.
This is not to say you should be complacent about a botnet infection. In fact you should do what you can to prevent and/or remove a botnet infection because there's a real possibility someone could use the data on your computer. Many botnets look for things like FTP passwords, so that they can upload code to your web hosting account. By already having code on your computer, a botnet infection could easily start monitoring your credit card numbers and other personal data too.
The other thing being part of a botnet does is contribute to a great deal of malicious behavior. Botnets are routinely used to interrupt service at large websites and steal customer data (possibly including yours) from big companies.
Having antivirus software is no guarantee that you'll stay botnet free. Avoid free offers inside Facebook and anything that sounds too good to be true. There aren't enough iPads in the world to fill all the promises of free ones I've seen go by on Facebook. It's a good idea to use some specific checks to make sure you aren't infected. In this case, the Koobface botnet reportedly has over 20,000 bogus Facebook accounts, along with half a million Gmail accounts. Malwarebytes is one of the tools you can use to make sure you're protected. While Malwarebytes is certainly not a botnet panacea, it will provide some protection from adding your computer to the zombie hordes.
Even if you think your safe, take the time to check out your computer. You'll be doing the global web community a favor. A free scan from some great software never hurt anyone.