Apple has decided to protect the App Store trademark.

According to TechFlash.com, Apple is planning to challenge Microsoft's complaint against Steve Jobs's company's registration of the App Store trademark, and has already filed a protest.

According to Apple's official letter, the term "App Store" isn't in common usage. However, Microsoft claims otherwise. According to company representatives, the phrase is a combination of two commonly used words: "App," meaning "application," and "Store," meaning "store," which are both commonly used.

Apple noted that Microsoft's trademark, Windows, is also a commonly used word, but this did not prevent the company from obtaining the exclusive right to use it in the operating systems market.

As a reminder, Microsoft filed a complaint with the US Patent and Trademark Office in June of last year. However, this only became public knowledge in early 2011. Apple opened its App Store in 2008. Besides Apple, other companies also own mobile app stores, including Microsoft (Windows Phone Marketplace).