Spam levels rose by 39 per cent during September, according to the latest figures from security firm SoftScan.

Junk email stopped by the firm's filters reached 93.51 per cent of all email during the month, tipping 98 per cent on some days.

Although virus levels remained relatively low, SoftScan noted a change in malware activity with a new virus attack each day.

"Since June this year we have seen an increase of 95 per cent in the amount of spam we stop each month," said SoftScan chief technology officer Diego d'Ambra.

"For organisations relying on spam filters alone, these past few months must have been a nightmare for network administrators."

With the exception of a few days at the beginning of September, when spam levels dropped to around 88 per cent, the remainder of the month has been consistently very high.

SoftScan predicted in August that spam levels would rise by 40 per cent in September as students returned to colleges after the summer break.

The company suggested that students' surfing habits make them an ideal target for malware writers.

Viruses accounted for just 0.14 per cent of email traffic during September, with phishing viruses topping the charts as usual.