Global computer experts are divided on whether the Sasser worm will now fade away, or become yet more of a threat.
The Sasser worm infects computers via the internet
Some believe the virus, which has wrought havoc on computers around the world, will slow down as more and more people fit additional security patches.
Yet others warn that Sasser could now merge with earlier virus-like programs to wreak yet more havoc.
Meanwhile the FBI has started to search for Sasser's creator, taking the Sasser code apart as it looks for clues.
"The infection is showing signs of slowing down, but the worm is still very active," said Ang Ah Sin, from security firm Trend Micro.
He said the outbreak was now largely contained because of the number of people who had now cleaned up their computers and upgraded their virus protection.
However, Jimmy Kuo from fellow firm Network Associates disagrees, saying Sasser could mutate and merge with previous computer virus Netsky to become even more of a problem.
"My expectation is that Netsky and Sasser variants will merge and become what we can one 'abundant threat' that attacks through email and software vulnerabilities," he said.
The Sasser worm first appeared on 1 May and between 150,000 and 1 million computers worldwide running on Microsoft Windows have been affected.
Machines at investment bank Goldman Sachs, the European Commission and British Airways and 19 regional offices of the UK Maritime and Coastguard Agency all fell victim to Sasser.
Up to 500 computers in hospitals in New Orleans were shut down for several hours and social and health services in Washington state were also hit by the worm.
The virus can infect PCs running Windows 2000 and XP that are not patched against the loophole it exploits or do not have a firewall to protect themselves.
According to anti-virus firms, machines running Windows 95, 98 and Millennium Edition can help spread Sasser even though they cannot be infected by it.