A game where players get to catch Osama bin Laden is driving AOL instant messager users up the wall thanks to its virus-style theft of email addresses and automatic forwarding.

The game, called "Osama Found", is an applet that Web users have to install but as soon as they do, the program grabs names from a user's AOL Instant Messenger address book and automatically sends those users instant messages with links to a Web page where the game can be downloaded.

However, what was no doubt viewed as a neat marketing ploy has drawn the ire of AOL users and now the company itself, with a spokesman telling us that the company is considering legal action.

Osama Found is not a virus or Instant Message worm but another example of what some call "adware," software that runs in the background on a computer and can be used by marketers to display advertisements and promotions on a user's desktop, said the AOL spokesman.

Once installed, the program allows the company that makes the game, PSD Tools LLC of Cambridge, Massachusetts, to send out what it describes as "additional content such as, but not limited to, advertisements and promotional messages to your computer and programs that may alter your home page to offer you content," according to a terms and conditions document that accompanies the installation program.

Also hidden in the terms and conditions for installing the program is language that allows the software to "interoperate with your current instant messaging client so as to permit the automatic sending of advertising messages originating from your Computer to your contact or 'buddy' list."

That may be a violation of AOL's terms of service, AOL's Andrew Weinstein said. Those terms prohibit using AOL Instant Messenger products to send unsolicited bulk communications or to authorise others to use an AOL IM account to do so, he explained.

AOL is investigating legal steps it can take to stop the distribution of the game. "We think this is a slimy piece of adware that we want to protect our users from," he said. AOL thinks the adware only targets AOL Instant Messenger users and will be updating its Instant Messenger home page with a warning about the adware and tips on removing it, Weinstein added.

Antivirus researchers at NAI's McAfee antivirus unit studied the Find Osama game and agree that it is not a virus or Trojan horse program, said Craig Schmugar, virus research manager.

The Find Osama game is similar in design to the so-called "friend-greetings" incident from October 2002, he said. In that case, an e-mail message inviting users to retrieve an online greeting card from the www.friend-greetings.com Web site tricked many e-mail users into installing an adware application.

The ruse demonstrates the importance of reviewing end-user license agreements carefully before installing new software programs. It also underscores the danger of downloading and installing unsolicited software, Weinstein said.