August 2003 was the worst month for virus attacks in history – and one virus may have switched off the lights on America's East Coast, according to the experts.

The W32.Blaster worm may have contributed to the cascading effect of the August 14 blackout on the US East Coast, reports Computerworld. It was also the second-most infectious virus last month.

On the day of the blackout, Blaster degraded the performance of several communications lines linking key data centres used by utility companies to manage the power grid, sources told Computerworld. Many control systems are based on Windows 2000 or Windows XP, the report states.

Online security specialist Central Command's VP products and services Steven Sundermeier observed: "August turned into a plague of Internet worms affecting computer users worldwide. Multiple aggressive worms made it the worst month in history for the number of infections reported, impacted organizations and lost productivity."

The Sobig.F worm was prevalent, accounting for 76 per cent of infections: "The extremely aggressive spreading nature of Sobig.F created significant volumes of email traffic causing email networks around the world to collapse. At its peak, Sobig.F related emails accounted for nearly 73 per cent of all email," said Sundermeier.

Sophos Anti-Virus' senior technology consultant Graham Cluley agreed: "August 2003 will be remembered as one of the worst months in the history of computer security," he said.

While Mac systems aren't directly affected by most reported viruses, users can receive unwanted email and even pass on viruses to others. Extra email and multitudes of spam have affected users on all platforms in recent weeks. Security speciallists recommend all computer users install anti-virus software, partially to prevent passing viruses on to others.

Cluley observed: "Bill Gates seems to be a target for hoax and virus writers alike. While the Blaster worm capitalized on a flaw in Microsoft's software and attempted to knock one of their websites out, hoaxes about Gates are circulating."

The Federal Bureau of Investigations (FBI) last week caught up with one virus writer, charging 18-year old Jeffrey Lee Parson with releasing a variant of the W32.Blaster worm on August 14. It is not clear if his version bought down the East Coast.

Parson has been banned from the Internet, had all his computers confiscated and will have to wear an electronic tagging device as he awaits trial on September 17.