The percentage of emails containing viruses remained at just 0.36 per cent during June, despite an attack launched by the Bagle virus.

The percentage of spam, however, was marginally higher month on month at 85.11 per cent, according to figures from anti-spam and antivirus firm SoftScan.

SoftScan considers this change to be the result of less business related email as the holiday season begins, rather than an overall increase in spam.

The company reported that a Bagle variant was spammed out over an 18-hour period on 21 June targeting some European countries.

In this latest development, Bagle was sent as a password protected zip file with the password sent as an image displayed in the body of the email.

SoftScan acknowledged that this made it more difficult for some antivirus vendors to detect the virus, but having to enter the password made many users think twice about opening the attachment thus preventing an epidemic.

The firm applauded the arrests in the UK and Finland of three men believed to be part of the M00P malware gang as a significant breakthrough in the fight against malware.

"The international police co-operation that led to these arrests is welcome news to everyone fighting against viruses," said Bo Engelbrechtsen, corporate communications manager at SoftScan.

"It sends a clear message that the internet does not necessarily offer the complete anonymity that some criminals think it does.

"Although it remains to be seen whether these arrests prevent the rest of the group from carrying on effectively, it demonstrates that chinks in their armour can be found."

SoftScan said that the top five email threats in June were phishing attacks (48.05 per cent), Netsky (16.69 per cent), Mytob (15.05 per cent), Bagle (5.94 per cent) and Mydoom (3.44 per cent).