A San Francisco network security company has started a campaign to name and shame corporate networks which host Trojan-infected PCs that send spam.

Support Intelligence has found infected PCs in many of the top companies in the world, including 3M, Toshiba, Bank of America, Borders and ClearChannel.

"We have been collecting data on the top 500 networks in Fortune 1000 companies evaluating how much spam or unsolicited commercial email they send," said the company. "We will continue this coverage until corporate America is clean."

Support Intelligence suggested that it will achieve this by 2012.

The data has highlighted some very poor security systems, even in technology companies.

Toshiba was singled out for particular criticism. Support Intelligence claimed that one of Toshiba's servers has been spewing out share ramping spam and bogus financial offers for over nine months.

By contrast, Borders suffered an infection and sorted it out within four days, and financial services company Charles Schwab was cleared of sending out any spam at all from its servers.

Support Intelligence will be naming companies on its blog for the next three weeks, showing IP addresses to prove its point.