Virus writers have developed a worm that spoofs the behaviour of internet search engine Google, varying the results displayed to suit the requirements of hackers.

P2Load-A modifies the HOSTS file on infected PCs by replacing the original with a file downloaded from a remote website under the control of hackers. When users run a search, the results are normally shown correctly - but sponsored links are different. For some searches, other links appear which have been specified by the creator of this malware, resulting in increased traffic to these websites.

The changes in behaviour happen because users are not getting their results from Google but from a hacker-controlled website based in Germany. P2Load-A also modifies a user's start page. Spanish anti-virus firm Panda reports the page is an almost exact copy of Google, which supports the 17 languages of Google and redirects users even if they make a mistake when entering the address, such as 'wwwgoogle.com'.

"Its [P2Load's] aims are none other than to increase visits to the pages linked by the creator of this malware or earn an income from companies that want to appear in the first few results in computer where the identity of Google has been spoofed," said Luis Corrons, director of PandaLabs. "In both cases, the motivation of the author of this malware is purely financial."

The worm spreads across file trading networks, targeting users of the Shareaza and Imesh P2P programs. P2Load-A copies itself to the shared directory of these programs as an executable file called Knights of the Old Republic 2, a reference to a well-known computer game related to the Star Wars saga. If this file is run, it displays an error message informing the user that a file does not exist and offering to download it. Meanwhile, unknown to its user, their Windows PC will have become infected.

PandaLabs has warned both the ISP hosting the page and Google in order to take measures and neutralise the attack. P2Load-A uses techniques for fooling users into visiting untrusted web sites more commonly seen in pharming attacks against DNS servers. Although it is rare for malware to change the HOSTS file of infected PCs the tactic is not unprecedented and has generated alerts from Australian consumer security firm PC Tools and others since the start of the year.