Given that the results come from a provider whose services promise to replace signature-based AV, and that the largest anti-virus software makers employ all kinds of filtering and behavior-tracking mechanisms, but a new report issued by SaaS security vendor ScanSafe finds Web threats taking off and many traditional forms of AV programs unable to catch them.

Web attacks leaped forward during Q1 2009, growing by just under 20 percent when compared to Q4 2008, which already one of the biggest months ever for growth of the threats.

ScanSafe reports that malformed image files, Adobe PDF and Flash attacks were the top of the charts during Q1 in terms of overall volume. The company reported that some 28 percent of the attacks that it observed during the period were more common forms of Trojans, while 35 percent represented those distributed by infected Web sites.

Perhaps the most significant trend over the course of Q1 was a jump in banking Trojans, ScanSafe researchers said. Many of the threats were somehow related to the Zeus botnet, which was implicated in a $6 milloin online bank theft carried out in Europe back in mid-2008.

Supercharged by an authoring toolkit named Luckysploit, Zeus has taken off anew, and is again growing its zombie network rapidly, according to the report. The toolkit has a particularly effective form of onboard encryption, making it difficult to choke off, with its orders coming from somewhere in Russia.

"Zeus bots are known for browser traffic sniffing, intercepting POST data and keystrokes associated with the active browser session as well as clipboard data pasted into the browser," ScanSafe explained in a report summary. "While these actions facilitate Zeus' activities concerning data theft, it could also lead to compromise of FTP credentials. For this reason, impacted sites may not just be spreading new Zeus banking Trojans and bots, their management systems may also be infected with previous variants of Zeus bots and banking Trojans."

ScanSafe contends that the conclusions are further exemplified by the fact that many Zeus-driven site compromises are being delivered via flat HTML-only sites, lessening the possibility that Web 2.0 exploits are involved in the campaigns. Zeus hallmarks also include an ability to circumvent signature-based AV and firewalls, and many rootkit-enabled variants.

Even before the Q1 takeoff, Zeus was believed to be resident on over 100,000 machines by ScanSafe's estimates. The company doesn't even chance a guess at how large the botnet might be right now.

The security experts said that backdoor and data thieving Trojans remain the second most popular attacks behind Zeus, some of which feature more highly customized payloads.

"The involved Trojans can be remotely custom configured by attackers and thus the exact data targeted and/or the specific action taken on the system can vary depending on specifics of the victim," ScanSafe said. "These Trojans also include the capability to intercept and tamper with http and network traffic. Data theft Trojans remain the most significant risk to enterprise users."

Matt Hines has been following the IT industry for over a decade as a reporter and blogger, and has been specifically focused on the security space since 2003, including a previous stint writing for eWeek and contributing to the Security Watch blog. Hines is currently employed as marketing communications manager at Core Security Technologies, a Boston-based maker of security testing software. The views expressed herein do not necessarily represent the views of Core Security, and neither the company, nor its products and services will be actively discussed in the blog. Please send news, research or tips to SecurityWatchBlog@gmail.com.