Popular file-sharing software from Grokster and the Limewire Gnutella Client contain the W32.DlDer Trojan, Symantec revealed last week.

According to several Reg readers, the KaZaA utility also contains the same infection.

The Trojan here is a spyware application masquerading as a lottery game called ClickTilUWin. When installing the Grokster or Limewire software, and some versions of KaZaA, the user is given an option to enable the ClickTilUWin feature. Regardless of whether one accepts or declines, the Trojan is installed.

Grokster has offered an explanation of this embarrassing oversight on its Web site:

"Some of you may be wondering why this Trojan was in our installer at all," the company speculates wisely.

"We sometimes bundle advertiser applications with our installer in order to help pay for our costs here at Grokster. We are normally given an installer from the advertiser which we run during the installation of Grokster. We have no access to the source code of these third-party installers and so we rely on what our advertisers say these programs do. To the best of our knowledge, this particular advertiser simply placed a link to a free online lottery on the desktop. We were never informed that it installed or was a Trojan."

The company has released a utility which it says will remove the Trojan, and promises to have a clean version of its software available in a matter of days.

Those who prefer to see to their own Trojan removal need only search for a hidden directory under their \Windows directory called \Explorer. Simply delete the \Windows\Explorer directory, along with the companion file Dlder.exe in the \Windows directory.

The Trojan is not destructive, but does phone home to the ClickTilUWin Web site with user data which, presumably, is used for marketing purposes, or is perhaps forwarded to RIAA headquarters to assemble a database of copyright scofflaws.

We don't know which; but we do know better than to install software we know nothing about. ®

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