A security flaw in Apple Mail that was fixed last year has returned from the grave to haunt those using the e-mail app in conjunction with the latest version of Apple's operating system, Mac OS X 10.5, otherwise known as Leopard.

An attacker exploiting the security flaw could create an e-mail attachment that appears to be, for example, a JPEG image file, but executes malicious code when it is clicked on, without the warning dialogue that should be present.

"In March 2006, Apple corrected this problem," says Heise Security on its Web site. "On a current installation of the Tiger OS, Apple Mail issues a warning that the supposed image file is a program and is to be opened with Terminal. Apple apparently either did not incorporate this update into Leopard, or did not do it correctly."

Apple's Security Update 2006-001 fixed the flaw. "In Mac OS X v10.4 Tiger, when an e-mail attachment is double-clicked in Mail, Download Validation is used to warn the user if the file type is not 'safe,' " Apple's Security Update explains. "Certain techniques can be used to disguise the file's type so that Download Validation is bypassed. This update addresses the issue by presenting Download Validation with the entire file, providing more information for Download Validation to detect unknown or unsafe file types in attachments."

An Apple spokesperson could not be reached because Apple is closed this week for Thanksgiving.

Last week, Apple released security updates for the most recent versions of its Mac OS X operating system, Panther, Tiger, and Leopard.