There's a major security hole in DNS -- and it is time to patch if you haven't yet.
Check if your ISP has patched their own DNS server by visiting Doxpara Research (the site of Dan Kaminsky, who found the problem a while back) and click on the DNS Checker on the right.
If you are running your own servers, be sure to check Microsoft Security Bulletin MS08-037 on patching them.
If you find that your DNS does NOT check out OK, try OpenDNS (you can see my original post on OpenDNS here). I use OpenDNS at home and at church, thus avoiding the entire problem in the first place.
In any case, run Windows Update to get the latest patches. It is a good policy.
For the geek-minded, here's an article about how the exploit was discovered.