Software giant Microsoft says it is confident it has thwarted threatened massive disruption to the internet from the MSBlast worm.
The virus threatened to bombard a Microsoft website
The computer virus was set to bombard one of Microsoft's websites from infected machines around the world on Saturday, raising fears it would paralyse the network.
Microsoft implemented a series of countermeasures and reported "no problems" hours after the attack was due to have begun.
However, variants of the worm have already appeared and more dangerous versions are expected in the coming weeks and months, says the BBC's Kevin Anderson in Washington.
In the first phase of its attack, the worm infected an estimated 300,000 computers worldwide, causing them to reboot frequently.
In the second phase, the computers were expected to fling data at the Microsoft website that helps Windows users patch their machines against viruses and other bugs.
However, a flaw in the worm may have enabled Microsoft to fend off its worst effects.
The worm instructed computers to call up http://windowsupdate.com - which is an incorrect address for reaching the actual Microsoft website that houses the software patch that protects against the worm.
Although Microsoft has long redirected those who visited that incorrect address to the real site, the company disabled the automatic redirection Thursday in preparation for the onslaught of infected computers.
Microsoft said its countermeasures had proved effective.
"We have been through a number of time zones now with no problems and we do not expect any as the [midnight Friday] deadline passes in the UK or US", said a Microsoft spokesman.
Microsoft said customers who have not yet installed software to remove the worm were still being affected by phase one of the virus' attack.