Internet users across the world are being urged to check their computers for malware - or else they may lose the ability to go online on Monday.
Warnings about the problem have been splashed across Facebook and Google (NasdaqGS: GOOG - news) , internet service providers (ISPs) have sent notices and the FBI has even set up a special website.
But hundreds of thousands of people around the world may still lose their connectivity unless they do a quick check for malware that could have taken over their machines more than a year ago.
Despite the repeated alerts, the number of computers that are probably infected is more than 277,000 worldwide, although it is down from about 360,000 in April.
Users whose computers are still infected on Monday may lose their ability to go online, and will have to call their ISPs for help deleting the malware and reconnecting to the net.
The problem began when international hackers ran an online advertising scam to take control of more than 570,000 infected computers around the world.
When the FBI went in to take down the hackers late last year, agents realised that if they turned off the malicious servers being used to control the computers, all the victims would lose their internet service.
So in a highly unusual move, the FBI set up a safety net.
It brought in a private company to install two clean internet servers to take over for the malicious servers, so people would not suddenly lose internet access.
But that temporary system will be shut down at 4.01am UK time on Monday.
Most victims do not even know their devices have been infected, although the malicious software has probably slowed their web surfing and disabled their antivirus software, making their machines more vulnerable to other problems.
FBI Supervisory Special Agent Tom Grasso said many ISPs are ready for the problem and have plans to try to help their customers.
He said they could either come up with technical solutions that they would put in place on Monday that would either correct the problem or provide information to customers when they call to say they have lost internet access.
If the internet providers correct the server problem, the internet will work, but the malware will still remain on victims' computers and could pose future problems.
In addition to individual computer owners, about 500 major companies are still infected, Special Agent Grasso said.
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 includes detailed instructions if users want to actually check their computer themselves.