A sophisticated cybercrime group that has maintained an especially devious Trojan horse for nearly three years has stolen the log-ons to more than 300,000 online bank accounts and almost as many credit cards during that time, a security company said today.Researchers at RSA Security Inc.'s FraudAction Research Labs tracked the Sinowal Trojan horse, also known as Mebroot and Torpig, to a drop server that contained the stolen credentials, said Sean Brady, the product marketing manager at RSA's ID and access assurance group."The sheer enormity of this makes this unique," said Brady. "And the scale is very unusual." All told, the gang behind Sinowal managed to obtain access to nearly half a million bank accounts and credit cards, a volume RSA dubbed "ruthless" and "extraordinary.""And the fact that the Trojan was managed by one group through its history and maintained for nearly three years is also very unusual," Brady said. RSA uncovered records that showed the Trojan horse had been in active operation since at least February 2006. "In malware life cycles, that's ancient, and to keep it up required a high degree of resources and effort."The company's researchers first got onto Sinowal's trail after they captured a sample of the Trojan horse. An analysis of its code laid out a map back to the drop server. That server was another unusual characteristic of the malware. "Infection points and drop points go up and down all the time," Brady said. "They typically have very short lifespans. But this drop site not only stayed up, it showed a sustained collection of log-ons."Brady also credited Sinowal's longevity to its authors' skills and secrecy.The Trojan horse has been revised more or less constantly, although there were periods when its creators ramped up the number of variants. After a lull last February, for example, the number of different versions again spiked in June, then hit slightly lower peaks in August and this month.The group is also more secretive than most, a trait that served it well. "They don't outsource, and [they] have all the necessary expertise in-house," said Brady. "They don't open their tool kits to other hackers, either. We suspect that the closed-loop nature of the group contributed to their ability to remain undetected."These crooks, like many at the top rungs of the cyberunderworld, work their craft first and foremost as a business. "We see some evidence that they have employed some practices that you may normally find in businesses that maintain high availability [of IT]," Brady continued. "They're using some redundancy, some backup effort for the data. They've clearly invested in this."Sinowal has infected hundreds of thousands of PCs worldwide during its run, and it continues to attack machines. Once on a system, the malware waits for the user to enter the address to an online bank, credit card company site or another financial URL, then substitutes a fake in place of the real thing. It's triggered by more than 2,700 specific Web addresses, a massive number compared with other Trojan horses.The fake sites collect log-on usernames and passwords to banks and other financial institutions and dupe users into disclosing information those organizations never collect online, such as Social Security numbers. The Trojan then transmits the stolen credentials and data to the drop server."This is one of the more sophisticated pieces of malware out there," said Brady.One reason Sinowal has been so successful is that it's rarely detected by antivirus software. "They struggle to find this one," Brady said. That's not surprising. The Trojan horse includes rootkit elements that infect the PC's master boot record (MBR), the first sector of a hard drive. Because the hardware looks to that sector before loading anything else, Windows included, the Sinowal is nearly invisible to security software. Security vendors have complained for months about how tough the malware is to spot.RSA Security suspects that the group responsible for Sinowal is based in Russia. "The distribution was truly global, but the one statistical anomaly that we noticed was [that] Russia was the one region that had no infections." Cybercrooks will often forgo infecting machines in their own country in the hope that local law enforcement authorities will not come calling or that if they do find out about the attacks, they'll put any action low on their priority list."This is the biggest find we've made to date," confirmed Brady. "But one reason why we're talking is so we can connect to [the affected] financial institutions." RSA has notified authorities and the banks and credit card companies with which it has existing relationships, but it needs help in contacting others, he said.