The so-called internet doomsday virus with the potential to black out tens of thousands of computers worldwide appeared to pose no major problems on Monday after a temporary fix expired.
Security firms reported no significant outages linked to the DNS Changer virus, as many internet service providers have either implemented a fix or contacted customers with steps to clean their computers.
The problem stems from malware known as DNS Changer, which was created by cybercriminals to redirect internet traffic by hijacking the domain name systems (DNS) of web browsers.
The ring behind the DNS Changer was shut down last year by the US Federal Bureau of Investigation (FBI), Estonian police and other law enforcement agencies, after infecting some four million computers worldwide.
Some 210 000 computers worldwide remained infected as of Sunday, including more than 41 000 in the United States, according to a working group monitoring the problem.
On Monday, temporary servers set up by the FBI to direct internet traffic normally, even for infected computers, were shut down.
But security specialists said most internet users and providers have had time to work around or fix the problem.
"Although it's not completely over, I think we can count case DNS Changer as a success story, said Mikko Hypponen, chief research officer at the Finland-based firm F-Secure, in a Twitter message.
"Many global operators are keeping their DNS Changer victims online, even after FBI stopped," he said in a separate tweet.
Johannes Ullrich of the SANS Security Institute said that for computers running Windows, the computer "may actually revert to the default settings once the DNS server is turned off."
He added, that "if you used the bad DNS server, chances are that various entities tried to notify you. Google for example should have shown you a banner."
Additionally, Ullrich said the malware is "old enough where antivirus, if you run any, should have signatures for it."
Six Estonians and a Russian were charged in Estonia in November with infecting computers, including NASA machines, with the malware as part of an online advertising scam that reaped at least $14-million.
Because the virus controlled so much internet traffic, authorities obtained a court order to allow the FBI to operate replacement servers until 9 July.