Spam continued at record levels in February 2007, making up 93 per cent of all email traffic monitored by internet security firm Postini.

The continued surge is primarily down to the increase in botnets, millions of hijacked PCs infected with malware designed to steal personal information and distribute spam and viruses.

Total spam levels have risen 222 per cent since November 2005, and 125 per cent of this increase has been recorded in the past six months.

Major email-borne virus attacks in January and February were aimed at creating more botnets for future attacks.

Heightened virus activity began in late December with the 'Happy New Year' spam attack and continued in January with the 'Storm' virus.

February saw a steady stream of attacks as hackers continued to harvest computers to add to their botnets.

This increase meant that February broke several spam records. Postini's global data centres processed more than two billion connections per day, and saw data volumes grow to more than 17 terabytes in a single 24-hour period.

Average volumes of spam blocked per day rose to more than one billion for the first time.

The dramatic increase in spam and internet attacks meant that the cost of dealing with the problem has skyrocketed.

A new study from Ferris Research predicted that the global cost of spam in 2007 will reach £53bn compared to £27bn in 2005. In the US alone, spam is expected to cost £18bn in 2007, up from £10bn two years ago.

"Following two of the largest outbreaks of email viruses in history in December and January, spam and other attacks reached all time highs in February, " said Daniel Druker, executive vice president of marketing at Postini.

"The rise of botnets has driven spam to £53bn business issue in 2007, making it [vital] for all companies to seek solutions that keep their communications safe and productive."

Postini believes that hackers are no longer relying on self-propagating internet viruses that copy and send themselves to the email addresses on the PCs they infect.

Instead, hackers are using botnets to launch spam attacks with viruses attached. In this fashion, the hackers are adding hundreds of thousands more computers to their botnets, and so the cycle continues.