Some 5 percent of computers are still infected with the Blackworm virus, which when activated can overwrite files, CiperTrust says.

The provider of messaging security says its research shows that most machines have been “disinfected”. However, CiperTrust warned that 18 percent of still-infected machines are in the United States.

“Although many machines have been disinfected, we’re certainly not out of the woods yet. Many machines may still be infected without their owner’s knowledge” said Dmitri Alperovitch, principal research scientist for CipherTrust. “Thankfully, the amount of media attention regarding the destructiveness and rapid propagation of the worm are accelerating action to block and remove the virus. This is particularly significant for that five percent of infected machines that could potentially be severely impacted on the third of next month.”