FAQ: Sheltering your systems from the Storm Worm

January 23, 2007 -- What is the Storm Worm?Not really a worm (it's actually a Trojan-bearing e-mail), but it's certainly a storm. Spotted in the wild on Jan. 17, the executable file reportedly infected more than 300,000 PCs within a week. That rate of infection would make this the worst outbreak since Sober.O back in spring 2005.
What are other companies calling it?F-Secure first identified the worm and called it the Storm Worm, based on its original subject line. Several aliases for the Trojan have been identified and grouped as Small.DAM. Other nomenclatures:
FrSIRT -- Downloader-BAI!M711 (via McAfee)McAfee -- Downloader-BAISophos -- Troj/Dorf-FamSymantec -- Trojan.PeacommTrend Micro -- TROJ_SMALL.EDW or CME-711Windows Live OneCare -- Win32/Nuwar.N@MM!CME-711
Which platforms are susceptible?Windows 95 and later, including Windows NT and Windows Server 2003. No Vista infections have been reported as of Jan. 23.
How does it infect?Mainly via spam, though it has been dropped on systems by other malware -- particularly WORM.NUWAR.CQ, a.k.a. W32/Nuwar@MM. That downloader has been used recently to drop other malware, particularly downloader-ARL.
What subject lines should I be watching for with that spam?They're changing rapidly to fit the latest headlines -- that's one of the things that makes this infection interesting.
The first subject lines concerned weather events in Europe -- hence the name. More recent subject lines mention severe U.S. weather, Chinese missiles, Russian missiles, Saddam Hussein (alive in some Elvis-like fashion), a purported terrorist attack on the Supreme Court and/or Congress, a paroled murderer in Michigan, and the always popular naked marauding teenagers.
Some quarters have reported finding the Trojan in romance-themed messages, presumably to take advantage of the Valentine's Day rush. An earlier infection dropped by the Nuwar downloader carried New Year's greetings, and the .exe claimed to be a greeting card or postcard.

A reader of F-Secure's "News from the Lab" blog points out that the latest list of subjects bears a resemblance to a list of cards in the romance category at 2000greetings.com, indicating that the perpetrators may be casting their nets even wider for "inspiration."
What's the payload?The message (in the case of spam) is accompanied by a compressed .exe file of about 29KB. The name of that file also varies, though not as much as the subject lines: Full Clip.exe, Full Story.exe, Video.exe, Read More.exe and other variations have been spotted.
If the user clicks on the file, a few things happen. The program installs two .ini files, peers.ini and wincom32.ini, and a system file called wincom32.sys. That's the Trojan, and it has rootkit capabilities (enabling the infection to disguise itself and its processes) to boot.
Once installed, the Trojan reaches out to a number of other machines, looking to download five files: TROJ_AGENT.JVH, TROJ_AGENT.JVI, TROJ_AGENT.JVJ, TROJ_DORF.AA, and WORM_NUWAR.CQ. (Note that, as mentioned above, Nuwar has been spotted as an infection vector for the Trojan itself.) It also opens up a slew of UDP ports, looking to make covert peer-to-peer-style connections to various IP addresses.
Interesting side note: BitDefender describes Trojan.Peed.P as containing the same three files and targeting a specific UDP port, 7871, for peer-to-peer connection purposes. That Trojan also uses a romantic-type subject line, and the payload claims to be a greeting card. However, that program's behavior appears to be significantly more aggressive -- sifting through address books, infecting genuine executables and attempting to shut down antivirus programs as well as regedit and taskmgr.
What's the best defense?If your e-mail filter is properly blocking inbound executables, you're fine -- as SANS's Mark Hofman puts it in his blog, "If you get a .exe in your inbox, something is seriously wrong with your inbound mail filter." In addition, antispam filters also appear to be stopping infected messages. If an infected file appears in your spam filter, it may be deleted with no further trouble.
If you're not filtering your e-mail or you find yourself cleaning up after someone who doesn't, user education is key: Never click on an executable file received in an e-mail, even if you think you know who sent it.
If you're infected, check with your antivirus vendor for system-specific solutions; most of them are on the case. Be advised that you'll have to dig out the rootkit, clean the registry (including the wincom32 autostart key) and delete the two .ini files. Don't forget to disable System Restore while you're scrubbing! Note that you should also check infected machines for WORM_NUWAR.CQ infection at this time