The FBI's not entirely sure. But they do know that some time ago, some hackers from Estonia ran a malware virus and infected somewhere north of 570,000 computers worldwide. Long story short, they'd make it so that when you tried to go to certain websites, you'd be routed through theirs, and the page hits would make them money. The thing is, once the hackers' servers shut down, your computer's access to the Internet shuts down too.
The FBI got those guys in November and shut down the servers. However, to keep people online, they put up something of a safety-net server to give themselves enough time to get a fix set up and to get the word out to everyone who's been infected to employ that fix. They were going to shut down those safety-net servers on March 8, but evidently, too many computers were still infected for it to be safe to do so, so the date's been pushed back to July 9.
The problem is best fixed online. So you really, really, REALLY want to make sure you're clean before that date.
The first thing you need to do is see if you're infected or not. Go here to find out. If not, great. Go ahead and go about your business (though noting that this may come up again in the future). If you are infected, the FBI suggests you either go here and find instructions to remove it, or alternately, call a guy and have him help you figure out what the heck you're doing.