Compiled by security business Sophos, the report for May shows an average of 9,500 new infected webpages were discoverered every day, including Government and other legitimate pages.

The figures show a 1,000-page a day rise on April. Overall, Sophos said it uncovered 304,000 webpages hosting malicious code last month.

A spokeswoman said:

"It's no longer enough for businesses simply to filter websites based on category - the real nasty attacks are often found lurking on legitimate webpages.

"This is a wake up call for organisations with a website: being out of date with patches and running inadequate security has very real risks."