At its height, the Sobig-F virus, which brought many company networks to a complete standstill, was responsible for a mind-boggling 73% of all email, according to figures released by anti-virus company Central Command.

Not surprisingly, it topped the charts of August's most prevalent viruses, but according to Graham Cluley, senior technology consultant at Sophos Anti-Virus, this does not tell the full story. 'The top four viruses are all new entries - any of which would have been number one in a normal month,' he said.

It highlights just how swamped the internet has become with viruses. And when combined with spam, businesses are up to their necks in internet-based security problems.

'Multiple aggressive internet worms made it the worst month in history for the number of infections reported, impacted organisations and lost productivity,' said Steven Sundermeier, vice president of products and services at Central Command.

The authorities are always one step behind virus authors and find them extremely difficult to track down. But last week, two alleged virus writers were arrested in relation to Blaster, August's second most prevalent virus.

Dan Dumitru Ciobanu, a 24-year-old Romanian and 18-year-old American Jeffrey Lee Parson, were arrested last week for their alleged roles in releasing separate variants of the same virus.

And the two could be facing a significant jail term as computer crimes in Romania carry a maximum sentence of 15 years' imprisonment, while American law could hand out a $250,000 (£158,168) fine along with a 10-year sentence.

According to analyst group IDC, businesses are being forced to spend more of their budgets on security as a result of the two viruses.

It claims that the virus attacks are fuelling spending, a trend that will continue to create a market worth $4.4bn (£2.8bn) over the next five years.

'The recent onslaught of viruses and worms such as Blaster, Nachi and Sobig highlights the need for antivirus products and, more importantly, the need to update services,' said Brian Burke, research manager at IDC's security products service.