Smaller businesses do not have adequate defences against the increasing threat from electronic attacks by terrorists, the British Chambers of Commerce has warned.

The fears come after a report found small and medium-sized British companies are increasingly vulnerable to pro-Islamic hackers who want to disrupt or destroy businesses.

Since May Islamic hacking groups have been working together and widening their targets, according to the leading internet security group mi2g.

In one week alone in October it found there were 124 attacks on British websites by one pro-Islamic hacking group.

Sally Low, Director of External Affairs and Policy at the British Chambers of Commerce, said the threat should be taken more seriously.

Problem intensifying Her organisation surveyed nearly 3,000 small and medium sized businesses about computer-related crime.

Of those that reported being victims of such crime most suffered from hacking and viruses. Others were affected by credit card fraud.

She said the problem had worsened as more and more businesses went online.

Smaller companies' links with larger customers and bigger companies, for example by putting on web links to their sites, made them more exposed to international viruses like the Code Red virus.

This virus affected hundreds of thousands of computers worldwide last year.

She called for an increased awareness of risk among small and medium sized businesses.

"Most businesses do not believe that they will be a target and they think their anti-virus software is sufficient," she said.

"They need to invest as much as they can possibly afford in ensuring that they have adequate firewall protection in place in their company.

"The cost in terms of lost revenue is significant and is increasing".

Mi2g works closely with government agencies and businesses to monitor computer hackers.