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More than ten million PCs worldwide that are remotely controlled by criminals through malicious executable files were distributing malware every day during the quarter two of 2008, it has emerged.

A recent study by PandaLabs and CommTouch found that the growing number of these "zombie computers" is the primary driver between the increased levels of spam being directed at users and companies, causing many businesses to require increased IT support.

The report showed that between April and June 2008, 74 per cent mail received by computer users was spam, adding that delivery methods remained relatively unchanged due to networks of bots - or "botnets" proving to be an effective method for criminals.

Luis Corrons, PandaLabs' technical director, noted that research by Nucleus Research found that receiving and deleting spam cost the average employee $712 (GBP 383).

He added: "This is not just annoying for users, who have to delete all of this mail, but in corporate environments it has important repercussions on productivity and resource consumption."

The Inquirer revealed today that malware-infected banners were spotted on big websites such as Digg, MSNBC and Newsweek, affecting all browsers that viewed them.

New research from Connect found that, on average, it takes businesses that use backup tapes take 11.6 hours to retrieve and restore files. Connect is now recommending that SMEs switch to www.connect.co.uk/services/online_backup