The Internet was quiet as the clock ticked past the scheduled start time for a massive, co-ordinated action by Microsoft Windows machines infected with the Sobig.F virus.
Beginning last Friday, anti-virus companies warned of possible danger posed by an unknown program that Sobig machines were programmed to download and run beginning at 1900 GMT.
Using atomic clocks associated with universities and governments around the world to co-ordinate their actions, the Sobig machines were scheduled to search a list of 20 Sobig.F servers that were individually hacked by the virus author and supplied with instructions to download and run a special file.
Security experts warned about the possibility of denial of service attacks, as thousands of Sobig-infected machines were all pointed to a single Web site.
Virus authors could also instruct the infected machines to download a Trojan horse program, giving the author a back door into the infected system for future use, experts said.
The CERT Coordination Center in the US and Europe as well as the US Federal Bureau of Investigation were informed of the threat and worked to notify the Internet service providers (ISPs) that hosted the machines named by Sobig so that they could be taken off line, director of antivirus research at F-Secure in Helsinki, Mikko Hyppönen, said.
That effort appears to have been successful.
"It's pretty quiet," said Johannes Ullrich, CTO of the SANS Institute's Internet Storm Centre shortly after the mass action was scheduled to begin. Ullrich did not notice any change in Internet traffic around the time Sobig was scheduled to download its instructions.
There were conflicting reports on Friday about whether all or just some of the Sobig servers were taken offline.
Network Associates (NAI) said that none of the 20 servers were online, a research fellow at NAI, Jimmy Kuo, said.
Internet Security Systems reported that one of the 20 was still online at 1500, but that no new instructions had been placed on the machine by the virus writer.
The last Sobig server stopped responding shortly after 1500, engineering manager at ISS, Dan Ingevaldson, said.
With few or none of the 20 servers accessible, Sobig machines were unable to download any instructions, experts agreed.
In addition, Internet backbone providers might have been asked to drop any traffic destined for those addresses, similar to steps taken to prevent a scheduled denial of service (DoS) attack against the White House that was programmed into the Code Red worm, Kuo said.
Such a move is standard procedure when Internet abuse and crime is tied to a specific machine or machines, according to Ingevaldson. In any case, once authorities began shutting down the IP (Internet Protocol) addresses of machines used by the worm, it was doubtful that the author would have risked uploading new instructions to one of those machines, Kuo said.
"My guess is the author saw how big and fast Sobig propagated and didn't want to go any further," Ingevaldson said.
Regardless of the outcome of the Sobig attack on Friday, future worms might well learn from the successes of the worm and incorporate that knowledge into future viruses, he said.