Solid Oak Software, the Santa Barbara, Calif.-based maker of Web filtering software called CYBERsitter, on Friday contacted the FBI to investigate a cyber attack on the company that appears to have come from China.

Earlier this month, the company charged that the Green Dam Web filtering software, made by two Chinese companies, contains its proprietary computer code. The Chinese government wants all PCs sold in China to include Green Dam starting on July 1.

Although the U.S. government and trade organizations have asked China to rescind its Web filtering rule, Sony has already begun shipping PCs with Green Dam installed.

Jenna DiPasquale, head of public relations and marketing for Solid Oak, said that following the receipt of suspicious e-mail messages sent recently to company executives and unexplained server problems, a Microsoft representative had volunteered to analyze the suspicious e-mail for malware.

A request for comment from Microsoft, submitted through DiPasquale, was declined.

But DiPasquale confirmed that Microsoft's investigator identified the messages as malicious. "They did determine that the files were infected and that the attack was specifically created for us," she said in an e-mail. "We discovered several one-off emails similar in nature that were caught by our filters. We do not know yet for certain, but it does appear that the e-mails are Chinese in origin."

Green Dam is made by Jinhui Computer System Engineering Co, and its Web filtering black list is provided by Beijing Dazheng Human Language Technology Academy Co.

The senders of the infected messages "used spoof-name Gmail accounts to create the attacks, and the documents sent were meant to appear like a clean e-mail," DiPasquale explained. "The infected documents referenced Jinhui and Green Dam and the attacks were written using Chinese language software. This is how we suspect that they are Chinese in origin. We discovered different types of attacks caught in our defensive gateway, AlliGate."