It all started last fall when six Estonians were charged with infecting more than four million computers worldwide with a malware virus that hijacked unknowing internet users, forcing them to a corrupted server that would send them to destination sites containing online ads.
"They had found a way to tap into one of the most lucrative sources of money on the internet, and that's online advertising," said Tom Grasso of the FBI.
Officials say the scam brought in more than $14 million and that those behind it were arrested, the corrupted servers taken over by the federal government.
Those servers were shut down at midnight, Sunday with 64,000 PC users in the U.S. at risk of losing their internet access.
"The good news is the odds aren't very high that you will be infected, but the bad news is if you are infected, you probably don't know," said Bob Sullivan, Technology Writer for MSNBC.
The FBI is telling those that were cut off to contact their Internet service provider for help reconnecting. Many providers already have plans to help their customers.
Another tip is to update antivirus protection and to install the latest version of Windows as malware is designed to resist detection and cleaning PC software.