Antivirus firms were forced to update their products to cope with up to 15 different strains of each of the worms, and thousands of users were caught in the crossfire.

Steven Sundermeier, vice president of products and services at Central Command, which said Netsky was responsible for over 70% of virus attacks last month, said: 'It wasn't really a question of 'if' we'll see another release, it was more of a question of "when".'

And Carole Theriault, security consultant at Sophos, agreed, adding that Netsky won the dubious accolade of the being the most prolific virus in March, accounting for almost 60% of all virus reports to Sophos.

'As the argument between the two virus writers escalated, a torrent of new worms was released,' said Theriault in a statement.

'To minimise the impact of such virus activity, businesses should consider blocking all attachments containing programs at the email gateway and setting up their antivirus protection to update automatically.'