Every week employees receive up to 30 chain letters, jokes, video clips or similar junk email messages from people they know, blocking up their corporate networks and slowing them to a halt, according to a survey.

Workers deal with more than 1,500 pieces of junk email each year from friends, family and colleagues. But spam, the much-reviled commercial email sent by strangers, is not set to reach the proportion of 'friendly' junk email until 2006.

The survey of 1,000 adults in the US with internet access, conducted for SurfControl by Market Facts, showed that junk email from friends causes just as many network headaches as commercial spam.

Internet research firm Jupiter Media Metrix predicts that by 2006 consumerswill be receiving an average of 1,400 pieces of commercial spam each year, or about 26 per week.

SurfControl's product marketing manager Paris Trudeau said: "Savvy companies understand the cost of commercial spam, but many have not yet considered the bottom-line implications of junk email."

"Junk emails, such as the 'teddy bear hug' and a host of prank, joke and game messages, carry huge payloads that can rob a company of valuable network resources and interfere with productivity," Trudeau said.

She added that sending one 5MB joke screensaver takes up the same amount of space on a company server as 160 plain text emails.