A line of USB drives sold by Sony installs files in a hidden folder that can be accessed and used by hackers, a Finnish security company charged Monday, raising the specter of a replay of the fiasco that hit Sony's music arm two years ago when researchers discovered that its copy protection software used rootkit-like technologies.

According to F-Secure, the fingerprint-reader software included with the Sony MicroVault USM-F line of flash drives installs a driver that hides in a hidden directory under "c:\windows". That directory and the files within it are not visible through Windows' usual APIs, said F-Secure researcher Mika Tolvanen in a posting to the company's blog Monday.

"[But] if you know the name of the directory, it is possible to enter the hidden directory using [the] Command Prompt, and it is possible to create new hidden files," said Tolvanen. "There are also ways to run files from this directory."

All of this -- and the fact that the directory goes unspotted by some anti-virus scanners -- is similar to the Sony BMG rootkit case in late 2005. Then, researchers spotted rootkit-like cloaking technologies used by the copy-protection software Sony BMG Music Entertainment installed on PCs when customers played the label's audio CDs. The Federal Trade Commission (FTC) alleged that Sony had violated federal law and settled with the company earlier this year. Before that, Sony paid out nearly $6 million to settle cases with U.S. states.

"This isn't the same code, recycled," said Mikko Hypponen, F-Secure's chief research officer, in an interview Monday. "Sony doesn't do any of its own development in this area; it looks like a Chinese company did it. But the similarities lie in the fact that like the Sony BMG rootkit, this software uses a hidden folder and hides files in it."

More important, he said, is another trait shared by both. "This can be used to hide malware," Hypponen charged.

By mid-November 2005, less than two weeks after the first reports that the Sony BMG copy protection software used rootkit-style technologies, Trojan horses using the Sony code to hide from security software popped up in the wild. Hypponen is convinced the same thing can happen here. "This will be trivial to use," he said.

Both Hypponen and Tolvanen pointed out that the MicroVault software is cloaking the folder for good reason: To protect the fingerprint reader's authentication files from being tampered with or circumvented. The issue, said Hypponen, is that Sony's left the door ajar. "What's not justified is that others can use this folder," he said. "If Sony was only hiding its own files, no one would object."

F-Secure first notified Sony "about a month ago" that its rootkit-sniffing software, BlackLight, had reported hidden files on a system with the MicroVault software. "We never got a reply," said Hypponen.

Sony did not respond to a Computerworld request for comment Monday.