For computer users, a few mouse clicks could mean the difference between staying online and losing Internet connections this summer.

Unknown to most of them, their problem began when international hackers ran an online advertising scam to take control of infected computers around the world. In a highly unusual response, the FBI set up a safety net months ago using government computers to prevent Internet disruptions for those infected users. But that system is to be shut down.

The FBI is encouraging users to visit a website run by its security partner, http://www.dcwg.org, that will inform them whether they're infected and explain how to fix the problem. After July 9, infected users won't be able to connect to the Internet.

Most victims don't even know their computers have been infected, although the malicious software probably has slowed their web surfing and disabled their antivirus software, making their machines more vulnerable to other problems.

Last November, the FBI and other authorities were preparing to take down a hacker ring that had been running an Internet ad scam on a massive network of infected computers.

"We started to realize that we might have a little bit of a problem on our hands because … if we just pulled the plug on their criminal infrastructure and threw everybody in jail, the victims of this were going to be without Internet service," said Tom Grasso, an FBI supervisory special agent. "The average user would open up Internet Explorer and get 'page not found' and think the Internet is broken."

MORE

chron.