The code's arrival comes just a day after Apple made an update available for its operating system. The malicious program takes advantage of a locally exploitable vulnerability in an operating system component called "launchd".
"Attackers may exploit this issue to execute arbitrary code with elevated privileges," Symantec said in a security alert to customers that was updated on Thursday.
On Tuesday, Apple delivered Mac OS X 10.4.7. The operating system update repairs a total of five flaws. Four of them affect both the client version of Mac OS X. The other, in the ClamAV antivirus software, has an impact on the server release.
Apple is recommending that people install all updates when they're issued to keep their software fully up to date, a company representative said Thursday.
"This proof of concept was fixed in Tuesday's Mac OS X 10.4.7 update," the representative said, referring to the ability for the exploit code to run.
The exploit was created by Kevin Finisterre, a security researcher at Digital Munition. Earlier this year, Finisterre created the Inqtana worm, which targets Mac OS X and spreads using an 8-month-old vulnerability in Apple's Bluetooth software. His actions are in part to demonstrate that Apple software is not unbreakable, he has said.
Apple users can download Mac OS X 10.4.7 through Software Update or the standalone installer. Typically, the Mac OS automatically checks for updates once a week.
Separately on Thursday, Apple put out iTunes 6.0.5, an update that it said fixes a security problem that could be used in a denial-of-service attack or let an intruder run code on vulnerable systems.
"The AAC file parsing code in iTunes versions prior to 6.0.5 contains an integer overflow vulnerability," the company said on its security Web site. "Parsing a maliciously-crafted AAC file could cause iTunes to terminate or potentially execute arbitrary code. iTunes 6.0.5 addresses this issue by improving the validation checks used when loading AAC files."
The iTunes vulnerability affects Mac OS X versions 10.2.8 or later and Microsoft Windows XP and 2000, Apple said.