The FBI's specialist cyber-crime unit has warned hackers off politically motivated revenge attacks on Middle Eastern websites.
The National Infrastructure Protection Centre (NIPC) has said that such attacks would be regarded as felony crimes, and that perpetrators could face five years in prison.
In a statement the NIPC said: "Those individuals who believe that they are doing a service to this nation by engaging in acts of vigilantism should know that they are actually doing a disservice to the country."
Hacker groups have been split on whether to take matters into their own hands following last week's attacks, with some issuing a call to arms and the appearance of defacements, such as at taleban.com.
The NIPC said that they expect hacker activity to increase and to see new computer viruses associated with the attacks.
A new version of the lifestages worm has already been reworked as WTC.TXT.VBS, it said.
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