Microsoft's decision to reduce the number of annoying security messages that Windows 7 delivers when users install software makes the new operating system more vulnerable to malware infection than Vista, a researcher said today.

"UAC was neutered too much by Microsoft," argued Chester Wisniewski, a senior security advisory with Sophos, talking about Windows' Users Account Control (UAC), the security feature Microsoft debuted with Vista.

UAC prompts users for their consent before allowing tasks such as program and device driver installation to take place. In an effect to quash user complaints which had condemned the constant intrusions, Microsoft modified UAC so it appears less frequently in Windows 7.

That wasn't a good idea, said Wisniewski.

"We wanted to know if UAC was going to be effective in Windows 7," he said. "So we grabbed the next 10 [malware] samples that came in and tried them out."

The 10 samples, most of them Trojan horses, were loaded onto a clean Windows 7 PC that lacked antivirus software, simulating payloads that an actual exploit would deposit on a compromised computer. Wisniewski then ran each piece of malware, as if a user had been duped into launching a file attachment or had surfed to a malicious site and been victimized by an drive-by attack and subsequent silent download.

Of the 10 samples, two would not run under Windows 7, not surprising since they were likely designed to execute on the far more common Windows XP and Vista, and only one of the remaining eight triggered an UAC prompt, said Wisniewski.

He acknowledged that the test was quick and dirty, and didn't accurately portray how secure Windows 7 was overall, or even how well it would withstand attack if protected by antivirus software, even basic programs like Microsoft's free Security Essentials. The point was to see how much Windows 7's reconfigured UAC would help block malware that made it past security software or got by other defensive measures of the operating system, like DEP (Data Execution Protection) and ASLR (Address Space Layout Randomisation).

"UAC is really not protecting users properly," Wisniewski said. "Frankly, people should turn it back into the more aggressive mode, like Vista," he said, speaking of the ability to set the feature's prompting frequency. "And if you find it annoying, you might just as well turn it off, because otherwise it's not doing any good."