By Joel Hruska
March 18, 2008 - 05:04AM CT

One of the factors that make an ongoing malware attack so difficult to stop is the speed with which the assault can evolve. Over the past 12 days, an IFrame injection attack that originally focused on ZDNet Asia has been spreading across the 'Net, changing targets and payloads on an almost daily basis. An iFrame (short for inline frame) is an element of HTML that's used to embed HTML from another source into a webpage.

The timeline of the attack is provided below, thanks in no small part to security consultant Dancho Danchev, who has kept a play-by-play account of the IFrame attack on his blog. This particular IFrame exploit takes advantage of web site query caching. Web sites often cache the results of search queries that are run locally. These search results are forwarded to search engine providers (think Google or Yahoo), who use the information to generate their own search results.

Hackers exploit the system by typing a query immediately followed by the text of an IFrame. This data (including the IFrame) is then passed to various search engines and displayed if a user searches for a relevant keyword. When the user visits an apparently legitimate document, the IFrame activates and attempts to complete whatever instructions it has been given. The major advantage of an injected attack versus an embedded one is that an injected attack requires no direct access to a web site's server backend.

Instead, it takes advantage of the company's SEO (Search Engine Optimization) practices and poisons the results that are fed back to web surfers. The first wave of injections targeted ZDNet Asia and torrentreactor.net. The attackers shifted away from these two domains quickly and branched out into other web sites. One key purpose of the attack was to advertise the rogue antivirus product developed by the RBN (Russian Business Network), XP Antivirus.