Steve Ballmer, the CEO of Microsoft, has admitted that Windows Vista was the "biggest mistake" he made, not just during his 13 years tenure as the CEO of the company but also in his entire time at Microsoft.

Ballmer admitted his mistake during a one-to-one interview with ZNet's reporter, Mary Jo Foley, in November-end.

In August this year, Ballmer announced that he has served his time in Microsoft and will step down as the CEO within 12 months. Since then the company is in the lookout for a suitable CEO.

Windows Vista, an operating system developed by Microsoft, was announced on July 22, 2005, and was known by the codename "Longhorn". Development of the operating system completed in November 2006 and it was released in January 2007.

The latest operating system was the successor to Windows XP, and was released more than five years after the introduction of its predecessor, which was the longest time span between successive releases of Microsoft Windows desktop operating systems.

Windows Vista included many new features but also received high criticism. The operating system required high system requirements, it had more restrictive licensing terms, it lacked compatibility with some pre-Vista hardware as well as software, and decreased the adoption rate as well as satisfaction rate when compared to Windows XP.

"When I look at it and I say, okay, what's the thing that I did that I feel -- that I regret the most, not just in my CEOship but my whole time here, it's absolutely 'Longhorn becomes Vista.' That was the single biggest mistake I made," Ballmer told in his interview.

"Not only because the product wasn't a great product, but remember it took us five or six years to ship it. Then we had to sort of fix it. That was what I might call Windows 7. And what we wound up with (was) a period of let's say seven or eight years where we had the A-team -- not all of the A-team but a bunch of our best people -- tied up not driving. We did not make years progress in eight years, and there were other things those people could have been working on, (like) phones," Ballmer added.

He also said that the Windows Vista was not just an executional mistake but it was also a technical strategy mistake. The company tried to fix the problem but could not succeed in attracting customers to the latest operating system.

Stephen Elop, ex-CEO of Nokia, who will join Microsoft as the Executive Vice President, Ford Motor Company's CEO Alan Mulally, Satya Nadella EVP of Microsoft's Cloud and Enterprise group, Tony Bates, EVP of Microsoft responsible for Business Development, Strategy and Evangelism and Steve Mollenkopf, COO and president of Qualcomm are rumored as the eligible candidates for Microsoft's top position.

Microsoft said it will announce its decision about Ballmer's successor sometime in early 2014.