Researchers at RSA report that a Trojan has quietly stolen login credentials from approximately 300,000 online bank accounts, a similar number of credit and debit cards, and an uncounted number of email and FTP accounts.

The Sinowal Trojan, also known as Torpig and Mebroot, has been stealing data for almost three years, RSA says. The new findings suggest that Sinowal "may be one of the most pervasive and advanced pieces of crimeware ever created by fraudsters," the researchers say in a blog published today. Little is known about Sinowal's source, RSA says. Some have alleged that it was owned and operated by a Russian online gang with past ties to the infamous Russian Business Network (RBN). "Our data confirms the Sinowal Trojan has had strong ties to the RBN in the past, but our research indicates that the current hosting facilities of Sinowal may have changed and are no longer connected to the RBN," the researchers say.

What's scary about Sinowal is that it infects victims' computers "without even an inkling of a trace," RSA says."The criminals behind Sinowal have not only created highly advanced and malicious crimeware, but have also maintained one of the most hidden and reliable communication infrastructures," the researchers say. "This infrastructure has been designed to keep Sinowal collecting and transmitting information for almost three years."

In addition, the stolen data has been methodically organized within a well-organized repository, according to RSA . And Sinowal has also been evolving at a dramatic pace -- its rate of attacks spiked upward from March through September of this year, according to the research.

Like other Trojans, Sinowal uses an HTML injection feature that effectively injects new Web pages or information fields into the affected victim's Internet browser -- and these injections seem like legitimate pages to the victim. "Sinowal is triggered by more than 2,700 specific URLs, which means that this Trojan quickly moves into action when users access the Web sites of what are now hundreds of financial institutions worldwide," the researchers say.

The RSA FraudAction Research Lab says it is currently sharing its findings with the appropriate parties. "We have disseminated large amounts of compromised data to some affected financial institutions," the researchers say. "We have also contacted several law enforcement agencies to inform them of our findings."