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May 7, 2009

F-Secure warns over Windows 7 security risk

Release Candidate ignores file extension threat

Gregg Keizer

Windows 7 Release Candidate (RC) continues a long-running Microsoft practice that puts users at risk, a security researcher said on Wednesday.

The new operating system's Windows Explorer file manager still misleads users about the true extension of a file, said Patrik Runald, chief research advisor at Helsinki-based F-Secure Corp. Rather than reveal the full extension for a filename, Windows Explorer hides the extension for known file types, giving hackers a way to disguise malware by using those file types' extensions and icons.

Windows Explorer, for example, will show the .txt icon and display 'attack.txt' as the filename for a Trojan horse that's actually been named 'attack.txt.exe' by the hacker. The practice goes back to at least Windows NT, and has been criticised in the still-popular Windows XP and the newer Windows Vista.

"People typically look at the icon to know what the file is," said Runald. "If it looks like a Word doc or a PDF file, there's an implicit trust in it, and users are more likely to click on those files, even if they are actually an executable."

Windows, Runald continued, is smart enough to know the true nature of the file, and will, for instance, run an .exe even if the filename shows as 'attack.txt' in Explorer.

"This has been used for years by virus writers - maybe less than it used to be, since most attacks now are drive-by downloads [using browser vulnerabilities], and not email attachments," Runald noted. "But you still see it."

Microsoft should show the true filename in Explorer, urged Runald. "Bottom line, it's a still bad idea not to."

Windows 7 RC launched yesterday, and will be available for download until at least through the end of July.

See also:

New Windows 7 features

Computerworld US

Free whitepaper: Phishing for victims - Truth, myth and cybercrime

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Comments received


billy said on Thursday, 07 May 2009

I have tried the new windows7rc and to me there is no diffrence between vista and windows7 windows7 has not got an anti virus support programe i have tried some free anti virus programes but i still got trojans in the windows7 as far sa i am concerned i will stick to vista at least you get anti virus programes to protect your computer

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