Just spreading the word on this. It is a DNS Changer that was created by hackers as an online advertising scam, that would make a users computer unable to access the internet.

Story here: http://news.yahoo.com/computer-infected-heres-fix-185144105--finance.html

Website to check if you are infected here: http://www.dcwg.org/ (just click on the green button in the upper left side called "Detect". The next page you can choose the location and language needed for you.
OR
You can just click on this site if you want the site in English and are in the US: http://www.dns-ok.us/

Thanks Pyonir - Last I read, March 8th was the close down time for the rogue DNS servers. I didn't know that more time had been allowed. The difficulty being that many compromised computers could lose their Internet connection quite suddenly if the rogue DNS servers were just seized and switched off. The reason for the time extension can be read about here:

http://garwarner.blogspot.co.uk/2012/03/dns-changer-countdown-clock-reset-but.html

Using a different DNS server to that supplied by the ISP can have benefits (providing it's not a rogue one of course). Some DNS servers filter out risky sites at source and put a block on them. Norton DNS and Comodo DNS will filter malware sites. OpenDNS is another choice but perhaps more geared for filtering out what might be considered 'non-family' sites.

The good part about using one of these servers is that they can give a layer of security that doesn't involve installing anything. Just a matter of changing a few numbers.

Norton provides a few different DNS numbers for filtering/blocking various sites:

https://dns.norton.com/dnsweb/faq.do#filtering_policies

Google also has a public DNS service: https://developers.google.com/speed/public-dns/

At one point, our cable internet provider's DNS server went down and had we used Google as the secondary server we wouldn't have lost internet service.