Microsoft Corp. has had to create a new build of Windows XP Professional for computer makers because the six-year-old operating system's continued popularity has nearly exhausted the supply of product activation keys.

The new build, dubbed SP2c, includes no fixes or feature changes, but was created simply to address the shrinking pool of product keys. XP Pro SP2c, which has been released to manufacturing, will be made available to OEMs and system builders next month, said Microsoft.

"Due to the longevity of Windows XP Professional, it has become necessary to produce more product keys for system builders in order to support the continued availability of Windows XP Professional through the scheduled system builder channel end-of-life (EOL) date," wrote the Microsoft system builder team on its blog Thursday.