Two UK men believed to be behind the TK worm have been arrested in Darlington and Durham.
According to the BBC, the men are understood to be members of a hacker group that calls itself 'THr34t-Krew'.
The group is thought to be responsible for the TK worm that used internet chat channels to attack other computers.
A 19 year-old electrician from Darlington and a 21 year-old man from Durham were arrested as part of a combined operation by the FBI and the UK's National Hi-Tech Crime Unit (NHTCU). They have been released on police bail.
Their homes were searched and computers taken away for examination.
The NHTCU said that the worm infected more than 18,000 computers and caused up to £5.5m worth of damage.
A spokesman explained that the worm infected machines by exploiting a vulnerability in Microsoft's IIS server software.
TK provides a backdoor into any computer and, once a machine is infected, it is reported to the 'tkworld' chat channels on IRC.
Infected computers could then be used to scan for other vulnerable machines or to launch proxy attacks.
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