(ABC News) -- Planning on using the Internet Monday? You might want to join the thousands of people who are checking their computers to make sure they won't lose connection.
The FBI's temporary Internet servers will go dark Monday, leaving thousands of unsuspecting malware-infected individuals without online access.
Why is this happening?
It all has to do with a piece of computer malware called DNS Changer. It started in 2007, when a group of hackers -- six Estonians and one Russian -- allegedly started masquerading as Internet advertisers who were paid by the click, according to an 2011 indictment from the U.S. Attorney General's Office in the Southern District of New York. In other words, if an ad got more clicks, they pocketed more cash.
So they figured out a way to beat the system, according to the indictment. They created a piece of malware, called DNS Changer, that tampered with the DNS -- the thing that takes a website address and finds the numerical IP address to connect you to that website -- redirecting millions of Internet users to sites they didn't search for.
For instance, if your computer was infected and you clicked a link to go to Netflix, you would wind up at "BudgetMatch," according to the FBI. The practice is called "click hijacking."
Once the FBI got around to fixing the problem in 2011, it realized it couldn't simply shut down the rogue servers because infected computers would be left without a functioning DNS, leaving them virtually Internet-less. So it set up temporary servers to give malware-infected Internet users time to fix their computers.
And time runs out on Monday, July 9.
(There isn't a planned attack this Monday that will shut down the Internet; those whose computers are already infected will lose the Band-Aid the FBI put on the problem more than a year ago.)
Who Is Affected?
Initially, there were more than 4 million infected computers in 100 countries, including 500,000 in the United States, according to the indictment.
As of July 4, there were only about 46,000 in the United States, FBI spokeswoman Jenny Shearer told ABCNews.com Sunday. (That's out of nearly 300,000 worldwide.)
PCs and Apple Macs have been infected. Routers and iPads were hit, too.
As of June, the United States had more infected computers than any other country, according to data from the DNS Changer Working Group, or DCWG, a group working on cleanup resulting from the malware.
How Do I Know if My Computer Is Infected?
You can check to see whether your computer is infected by clicking on this link, which is run by DCWG.
If the page is green, you're in the clear. If it's red, your computer is infected.
On Thursday the site got 2 million hits, but very few of those computers were infected, DCWG volunteer Barry Greene told ABCNews.com.
Google and Facebook say they have also set up notifications for infected users. If you type in a search term and see a message that says, "Your computer appears to be infected" at the top of your screen, guess what. Your computer is infected.
Comcast, AT&T and Verizon are among the other organizations notifying customers if they have infected machines.
Important: According to DCWG, you should not need to scan, make changes or download anything to tell whether your computer is infected.
My Computer Is Infected. Now What?
The good news is DCWG has put together a page of trusted tools and a step-by-step guide for how to fix your computer.
The bad news is it can take a day or two actually to fix the problem, Greene told ABCNews.com.
That's because the malware is in a deep section of the hard drive called the "boot sector."
"The malware problem out there is nasty, and it's impacted society on multiple levels," Greene said. "It's extremely hard to get rid of. In most companies, if they get infected with it, they throw away the hard drive."
If you can't do that, follow the instructions. They include backing up your files and reinstalling your operating system.
What Do I Do if I Lose Internet on Monday?
The FBI and DCWG recommend contacting your Internet service provider. They'll be able to give you instructions on what to do next.
For more on this story, go to ABCNews.com.