'Tigger' Trojan Keeps Security Researchers Hopping

It's malware that actually removes other malware from its victims' PCs. And so far, nobody is exactly sure how it's being distributed.

Security experts this week are buzzing about a new Trojan called Tigger.A, also known as Syzor. The data-stealing malware has quietly claimed about 250,000 victims since it was first spotted by security intelligence company iDefense in November, according to a Washington Post report.

Tigger.A allows attackers to gain access to "administrator" privileges on Windows machines, even if the user himself doesn't have those privileges, according to the report. It takes advantage of a vulnerability (MS08-066) in Windows' "privilege escalation" feature that Microsoft revealed -- and patched -- in October.

"Tigger removes a long list of other malicious software titles, including the malware most commonly associated with Antivirus 2009 and other rogue security software titles," the report says. "iDefense analysts say this is most likely done because the in-your-face, "Hey, your-computer-is-infected-go-buy-our-software!" type alerts generated by such programs just might tip off the victim that something is wrong with his system, and potentially lead to all invaders getting booted from the host PC."

The Trojan also installs a rootkit on the infected system that loads even when the system is started up in safe mode, iDefense researcher Michael Ligh says in the report. "The scary part is, none of us are really sure how Tigger is even being distributed," he said. "I look at a lot at info-stealing malware, and this is the first one I've seen in a while that goes to the trouble of removing other pieces of malware."

Tigger's ability to collect user data also is impressive, IT expert Michael Kassner notes in his blog.

"The Trojan uses a privilege escalation vulnerability which is almost an exact replica of the public exploit on Milw0rm," the blog observes. "It disables Windows Defender, Windows Firewall, Outpost, Avira, Kaspersky, AVG, and CA products in unique ways such as posting malformed messages to windows owned by the daemon processes, sending special byte codes over named pipes, and using the products' own API. It installs a rootkit that runs in safe mode [and] disables kernel debuggers.

"Tigger, of course, also injects code into user-mode processes," the blog states. "This component takes screen shots, hooks COM for spying on browser events, and exports passwords [from] protected storage, network and dial-up, and at least 11 popular chat, email, and remote access applications. It also steals web cookies, steals certificates, and puts the NIC in promiscuous mode to sniff FTP and POP3 passwords."

The Trojan also logs keystrokes, collects system information, and enables a backdoor on compromised computers, according to research data posted on the Threat Expert Website. It may also attempt to initiate communications with command and control servers.

So far, Tigger is targeting a small list of users, mainly customers or employees of stock and options trading firms. Among the list of targeted institutions are E-Trade, ING Direct ShareBuilder, Vanguard, Options XPress, TD Ameritrade, and Scottrade. Experts in the financial services industry are warning brokers and day traders that their systems may be at risk.

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