The vulnerability, which carries a "moderately critical" rating, is caused by an error in the way the application parses the parameters passed by the URL handler.
"This can be exploited to initiate the transfer of a file from one Skype user to another via a specially crafted Skype URL without requiring the sender to explicitly consent to the action," said a warning from flaw alerts aggregator Secunia, based in Copenhagen, Denmark.
Skype, which is owned by eBay, in San Jose, Calif., acknowledged the issue and released new software versions to provide patches to millions of users.
Skype said the attack requires the targeted user to manually follow a specially crafted malformed link, as might be found on a Web page.
Depending on several factors, doing so could result in the initiation of a file transfer, which would be accompanied by the normal Skype file transfer dialog box, the Skype advisory said.
"If a file transfer is started, it will be visible to the user and may be cancelled by the sender by selecting Cancel in the normal way," the advisory said.
Skype 2.0 and Skype 2.5 for Windows are affected by the flaw.