The wave of attacks began early last week targeting corporations in the form of email messages that alerted victims of a "system upgrade." Email is accompanied by poisoned attachments and links; in some cases it poses as a message from victims' IT departments, including their actual email domains, and alerts them about a "security upgrade" to their email accounts. The message then refers victims to a link to reset their mailbox accounts, and the link takes them to a site that looks a lot like an Outlook Web Access (OWA) page (PDF), but instead infects them with the Zeus Trojan.
Today, researchers at F-Secure spotted the botnet spamming out malware-laden email that tries to trick recipients with a convincing lure messages that says, "On October 22, 2009 server upgrade will take place."
"What we're seeing is an evolving campaign of different lures to see which one works," says Richard Wang, manager of Sophos Labs in the U.S.
The Zbot botnet, which is made up of 3.6 million PCs in the U.S., or 1 percent of all PCs in the country, according to data from Damballa, spreads the deadly Zeus Trojan. Zeus, which steals users' online financial credentials, represents 44 percent of all financial malware infections today, according to Trusteer.
But according to Trend Micro's Paul Ferguson, the Zbot botnet isn't actually behind the latest attacks: it's the fast-flux Avalanche botnet, which is hosting Zeus and Zbot Trojans.
The Shadowserver Foundation has seen multiple versions of Zeus-related attacks lately, including the Conficker "cleanup utility" that poses as an email from Microsoft, according to Andre DiMino, director of Shadowserver. And the targeted Outlook attacks use real domains: "What is also interesting about the recent campaign is that the email comes from the targeted user's own domain with an 'administrator' prefix. The link is disguised to look like it's from an update server on the local domain, but instead points to the malicious location," DiMino says.
Amit Klein, CTO at Trusteer, says the Conficker phishing email was pushing fake antivirus software and, in some cases, also contains Zeus, so he's not convinced that attack is necessarily coming from the same gang behind the Outlook and other phishing campaigns. "I really don't know" if it's the same Zbot botnet behind those two attacks, he says. "But if it's spreading the same malware with a similar concept [of a phishing attack], it does raise suspicion that the two events were by the same gang, or it could be a copycat."
The Outlook attack was the first large-scale Zeus attack against the corporate world, he says, which signals a new strategy for Zbot. "Shifting its focus there makes a lot of sense for financial malware because the typical credentials you can steal from the corporate world are worth a lot more money than credit cards and accounts in the consumer world. To own the company's accountant or finance department's bank account credentials would be a lot more profitable," Klein says.
Zeus traditionally has been one of the more difficult malware variants for some antivirus programs to detect: According to recent data from Trusteer, Zeus is detected only 23 percent of the time by up-to-date antivirus applications. It's also hard to kill because it hides itself so well in the operating system.
Trusteer's Klein says this new wave of phishing attacks from Zbot is just the beginning. "These are new flavors, and we're going to see a lot more of these in the future," he says. "This has proved to be highly effective."
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