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Bank Trojan crooks trouser £800k from 30,000 Brits

How the crims outran anti-virus sniffer dogs

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Analysis Trustwave SpiderLabs has revealed how criminals stole more than £800,000 (€1m) from UK bank accounts using the Zeus Windows PC malware.

The scam - which ran from June to November last year - targeted customers of six banks in Britain. It began with a flurry of emails that tricked marks into clicking on a link to a fake Facebook login page on the crooks' servers.

The bogus website then offered to install a Flash plugin upgrade that contained a bot, a piece of software that allows a hacker to control a compromised machine. Even if a victim refused to take the update, the page used the Blackhole kit to detect the computer's security vulnerabilities and exploit them to install the electronic nasty if possible.

Once in place, the bot hides itself from view and downloads the Zeus Trojan to silently install. This piece of malware then interferes with the victims' online banking transactions to quietly redirect money to "mule" accounts.

Users within the UK were specifically targeted using geo-fencing techniques that identified their location based on their internet connection. Machines in South America white listed to protect them from infection as were test machines and affiliates in the criminals' network.

Ziv Mador, director of security research at Trustwave SpiderLabs, explained that the crooks behind the assault had used the same server in Moldova associated with a previous Zeus-powered scam, which was detected in August 2010. This operational security mistake allowed his analysts to obtain access to logs and other information that allowed them to profile the attack.

Trustwave found that the money thieves managed to infect approximately 30,000 PCs, the majority of which are in the UK. The malware used more advanced cloaking techniques than the previous assault so that it could communicate with command-and-control servers while remaining undetected. In addition, the 2011 attack was on a greater scale than its 2010 predecessor and involved several affiliates, each launching bots of their own.

Detection rates of the Trojan by anti-virus software throughout the run of the attack was low and consistently under 20 per cent, according to Mador. The crooks tweaked the malware delivered via the attack every couple of days in order to outpace detection.

The brains behind the fraud

"The unique thing about this attack was the algorithm to mask transactions," Modor told El Reg regarding the way in which the thieves siphoned cash from victims' accounts. "The cybergang maintained a database of money mules and they wouldn't use a money mule again, at least until a transaction had cleared. There was a lot of automation."

The 2011 attack was carried out using the Smoke Loader tool, which centrally manages the network of compromised computers, as well as the Blackhole exploit kit; the 2010 attack relied on the less sophisticated Elixir toolkit. Each kit tries to automatically install a payload of malicious software when a victim visits a booby-trapped website by exploiting security holes in web browsers, Java runtimes, Flash players and other software.

Trustwave SpiderLabs handed its research to UK police last year. It published a series of articles into the technical details of the attack after getting the go ahead from cops, who were satisfied that disclosing this information would not compromise their investigation.

It is unclear whether any arrests have been made over this particular scam, which is all too commonplace.

The blog posts by Trustwave SpiderLabs on Zeus can be found here: part 1, part 2, part 3, part 4 and part 5.

Each is full of technical descriptions and code analysis for those that way inclined.

Meanwhile, Microsoft has named two alleged ringleaders in a banking scam that relied on the Zeus Trojan: Ukranian nationals Yevhen Kulibaba and Yuriy Konovalenko, who are serving time in UK prisons following convictions last year and now face possible US extradition proceedings.

McAfee has also published details of a £60m attempt to target the bank accounts of the well-heeled. Operation High Roller used SpyEye and Zeus, man-in-the-browser techniques and automation comparable to the Zeus caper chronicled by Trustwave SpiderLabs, but was arguably even more sophisticated. ®

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