The agency says over recent months it has seen numerous situations in which fraudsters have gained access and stolen funds from online brokerage accounts, in some cases using keylogging programs to steal user names and passwords. Some individual investors have lost hundreds of thousands of dollars after failing to protect their PCs from cyber-thieves.

The regulator has now issued an investor guide outlining steps that can be taken - such as installing a firewall, using a security token and ignoring e-mails that request confidential information - to secure online brokerage accounts from intruders.

"We are concerned that many investors aren't taking appropriate precautions when accessing their online brokerage accounts," says SEC investor education director Susan Wyderko. "In our guide, we offer tips on how online investors can protect their personal information from intruders."

Last year the SEC successfullly prosecuted an online investor who used a Trojan Horse program to hack into a third party brokerage account to purchase his own expiring stock options in an attempt to avoid losses on them. Van Dinh of Massachusetts is the first person to be prosecuted by the SEC on computer hacking and identity theft charges.