Experts say about 45 thousand computers in the U.S. are infected with the DNS Changer malware, and computer owners may not even know it.
On Sunday night the FBI shut down computer servers that were preventing the malware from taking over your machine.
About a year ago the agency busted computer hackers who sent out the DNS changer to computers all over the world.
Agents learned shuttung down the servers running the malware program would eliminate internet service to infected computers.
"What they did was, sort of, put up a temporary server to allow people to have time to get their machines clean," Travis Tidwell of Nerds on Call said.
Tidwell runs the Nerds on Call office in Northwest Fresno. He spends his days removing viruses and other malware from personal computers.
"The biggest reason why people tend to get viruses is they allow their anti-virus to lapse. They don't keep it up to date," Tidwell said.
He says the hackers were using the DNS changer in an effort to gain access to your personal information. That's why current anti-virus software is important.
It could keep hackers like the ones who created DNS Changer from stealing your private information.
"Anytime you go into any websites and you're downloading anything that's free , like free screen savers and free child's games, you can get infections that way. That's why having that line of defense, the anti-virus, is important," Tidwell said.
There are websites you can click on to check if you're computer is infected.
You should get a green screen if you're okay. It would be red if you're infected with the DNS changer.
So if you can't get online from your computer it may be a result of the DNS changer.
In that case, Tidwell says you will likely need to have your computer scanned with anti-virus software or take it to a professional.
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To check whether a computer is infected, users can visit a website run by the group brought in by the FBI: http://www.dcwg.org .
The site includes links to respected commercial sites that will run a quick check on the computer, and it also lays out detailed instructions if users want to actually check the computer themselves.
Click here to check and clean computers.
Nerds on Call: DNSChanger: How To See If You're Infected, How To Fix It If You Are
