Microsoft has released free security software for Windows. But the company has confirmed it will only work with legitimate copies of the operating system.

The software, once codenamed Morro, is now known as "Security Essentials." It's a replacement for OneCare, a previous Microsoft security product that was not free.

Effective, but Falls Short of Rivals

Independent tests of the finished product suggest it's a useful tool, though falls short of the protection offered by commercial rivals. One company testing it found Security Essentials detected 98.4% of malware and 90.9% of spyware. Impressively, it picked up all 3,700 security threats when run against a database of the current most common threats. (Source: computerworld.com)

However, the software does have some limitations. It can only track down threats by matching the relevant files to its database, rather than using "heuristic" techniques which also look for suspicious behavior. It also struggles to remove all traces of some viruses and doesn't automatically switch the Windows firewall back on when it's been disabled by a virus.

No License, No Protection

In somewhat of a surprise, Microsoft has announced that Security Essentials will only work on legitimate copies of Windows. While installing the software, a user will need to go through a brief validation process which automatically checks if they are running a valid copy of the operating system. (Source: windowsteamblog.com)

Making the software exclusive to legitimate Windows users would not have been an easy decision. At first glance it seems obvious that only people who've paid for the software would deserve the freebie.

Viruses Don't Discriminate Pirates

From a practical standpoint, however, some might argue this theory is half baked considering that it will inevitably look bad upon Microsoft for allowing any virus to infect and spread onto other Windows systems -- whether the user owns a pirated copy of Windows or not. It's also arguable that security software is most needed in regions where piracy is rife because computer users are as much unable as unwilling to pay for protection.

The decision is not typical Microsoft policy: the firm does allow people running pirated copies of Windows to still receive automatic security updates for the system itself. However, in that situation Microsoft is the only source of those updates, whereas other antivirus products, both free and paid, are available.