The millennium date change will be used as a cloak by hackers and cyber terrorists to mount attacks against corporate networks, security experts warned last week.

The warning came as evidence emerged from US cyber activist Ricardo Dominguez that the radical Reclaim the Streets group sought advice on sabotaging computer sites and recruited teams of UK based hackers.

The group aims to increase the network damage caused by protests it organised on 18 June (J18), when hackers used Floodnet to block or crash Websites in the City of London. For five hours at least, 20 companies were subjected to more than 10,000 attacks by hackers.

Ex hacker turned consultant at Tiger Security, Mathew Bevan, warned that network managers should expect the worst from opportunist or planned attacks.

"People don't know who Year 2000 contractors are, so how can they trust their code? There is proof the Mafia was backing hackers posing as year 2000 programmers," said Bevan. "People will have hacked some machines and no one will know until too late."

Malcolm Skinner, marketing director at Axent Technology, said: "There will be an enormous amount of hacking activity camouflaged by Year 2000 issues."

Skinner said hackers intend to disguise attacks so that they look like a series of unrelated incidents. Unwary network managers would dismiss even sustained attempts to take ownership of systems as simple Year 2000 glitches.

DK Matai, managing director of software consultant Mi2g, which works with a number of City firms, said the biggest risk comes from Trojan Horse programs which may be activated when network managers disable security protocols to carry out Year 2000 network diagnostics.

The threat is being taken seriously by the banking community. The British Bankers' Association has issued a Planning Guide for the Millennium, advising extra security precautions over the period.

For more stories see this week's issue of Network News UK