A CIA report has warned that a number of terrorist groups are hatching plans to attack Western computer networks.

The report, which is a response to a list of questions from a US senator, names Sunni extremists Hezbollah and Aleph as groups believed to be developing cyber terrorism plans.

The report claims that the CIA is "alert to the possibility of cyber warfare attack by terrorists on critical infrastructure systems that rely on electronic and computer networks".

It added that attacks against critical infrastructure systems will become an increasingly viable option for terrorists, as they become more familiar with these targets and the technologies required to attack them.

The report identifies al-Qaeda and Hezbollah as becoming "more adept at using the internet and computer technologies".

"The FBI is monitoring an increasing number of cyber threats and the sort of groups most likely to conduct such operations include al-Qaeda and the Sunni extremists that support their goals against the US," said the report.

Aleph, formely known as Aum Shinrikyo, is the terrorist group that places the highest level of importance on developing cyber skills.

"This group identifies itself as a cyber cult and derives millions of dollars a year from computer retailing," the report stated.