When Microsoft announced the successor to Windows 8 will be called Windows 10, most of us wondered what happened to Windows 9. Now a self-professed Microsoft developer has suggested the reasons might date back to the last millennium.

During the presentation to announce the new system, Microsoft didn’t give any clear explanation, but hinted at two possible reasons:

* They wanted to put it across as a major development rather than just a case of fixing problems from Windows 8 (in the same way as 7 did for Vista.)

* They’d really rather have called it Windows One to fit the “running on every device” theme, but that might cause confusion.

Some other theories, of varying levels of credibility, include that the number nine is unlucky in Japan (the translated number sounds close to the word for torture), and of course that dad joke classic that it’s as simple as that seven ate nine.

However, a man claiming to be a Microsoft developer has posted on Reddit to share an internal rumor that it’s actually because many independent applications are coded to check for compatibility with past editions and that code uses “Windows 9” as a short way to search for both Windows 95 and 98. The example given was:

if(version.StartsWith(“Windows 9”))

{ /* 95 and 98 */

} else  {

Crazy as the idea might sound, several people have carried out searches on code databases and found examples, such as with Java, where there’d be a risk of confusion and resulting software problems.