At least two mutant variations of the "Code Red" computer worm have been attacking US and British computer networks, possibly infecting thousands more terminals, Internet security experts have warned.
"We are aware of at least two variants of the computer worm making their way now," Ms Debbie Weierman, a spokeswoman for the FBI's National Infrastructure Protection Center, said.
She added that the worm had been first discovered late last week, but declined to provide details beyond saying: "We are currently assessing the situation."
Meanwhile, the Symantec AntiVirus Research Center, a private Internet security firm, identified the worm as "Code Red.C."
It said it was first discovered on Saturday and is deemed to be a variant of the original "Code Red" worm that has been ravaging US computer networks since last month.
The center said it had received reports of "a high number" of Web servers infected.
"We are assessing "Code Red.C" to be a high threat," the centre said in a statement.
A similar mutant worm was reported yesterday by the British Home Office.
The original "Code Red" worm, which infected 250,000 systems in the United States in just nine hours in mid-July, made its way into the system by first scanning the Internet, identifying vulnerable terminals and infecting them by installing itself, according to experts.
AFP