Microsoft has released Microsoft Safety Scanner, a no-install anti-malware program designed for one-off malware scans and removal.

Unlike the previous variants of this fake antivirus, no administrator's password is required to install this program. Since any user with an administrator's account - the default if there is just one user on a Mac - can install software in the Applications folder, a password is not needed. This package installs an application - the downloader - named avRunner, which then launches automatically. At the same time, the installation package deletes itself from the user's Mac, so no traces of the original installer are left behind.

Data released today by Microsoft showed that Windows 7's malware infection rate climbed by more than 30% during the second half of 2010, even as the infection rate of the 10-year-old Windows XP fell by more than 20%.

"Infection rates have jumped [for Windows 7]," admitted Jeff Williams, the principal group program manager with the Microsoft Malware Protection Center (MMPC). "We attribute that to the increased presence of malicious software attacks out there."

For the second half of 2010, 32-bit Windows 7 machines were infected at an average rate of over 4 PCs per 1,000, a 33% increase over the approximately 3-per-1,000 infection rate during the first half of the year.

PCs running the 64-bit version of Windows 7 fared slightly better, with an infection rate of 2.5 per 1,000 during all of 2010.

Snow Leopard lacks security features that are built in to Windows XP, Windows Vista and Windows 7, a noted Mac researcher has said.

Dubbed ASLR, for address space layout randomisation, the technology randomly assigns data to memory to make it tougher for attackers to determine the location of critical operating system functions, and thus make it harder for them to craft reliable exploits.

"Apple didn't change anything," said Charlie Miller, of Baltimore-based Independent Security Evaluators, the co-author of The Mac Hacker's Handbook, and winner of two consecutive "Pwn2own" hacker contests. "It's the exact same ASLR as in Leopard, which means it's not very good."

Two years ago, Miller and other researchers criticised Apple for releasing Mac OS X 10.5, aka Leopard, with half-baked ASLR that failed to randomise important components of the OS, including the heap, the stack and the dynamic linker, the part of Leopard that links multiple shared libraries for an executable.

Miller was disappointed that Apple didn't improve ASLR from Leopard to Snow Leopard. "I hoped Snow Leopard would do full ASLR, but it doesn't," said Miller. "I don't understand why they didn't. But Apple missed an opportunity with Snow Leopard."

Because Snow Leopard lacks fully-functional ASLR, Macs are still easier to compromise than Windows Vista systems, Miller said. "Snow Leopard's more secure than Leopard, but it's not as secure as Vista or Windows 7," he said. "When Apple has both [in place], that's when I'll stop complaining about Apple's security."

In the end, though, hacker disinterest in Mac OS X has more to do with numbers, as in market share, than in what protective measure Apple adds to the OS. "It's harder to write exploits for Windows than the Mac," Miller said, "but all you see are Windows exploits. That's because if [the hacker] can hit 90% of the machines out there, that's all he's gonna do. It's not worth him nearly doubling his work just to get that last 10%."