Apple has announced it is aware of a bug many iPhone users are experiencing with iMessage since upgrading to new mobile operating system iOS 7, the Wall Street Journal reported.

Apple described the iOS 7 upgrade as the biggest overhaul from one mobile operating system to the next in the history of the iPhone. It featured many changes including the addition of a settings control center, a redesign of mobile browser Safari, an upgrade to Siti, AirDrop and a completely redesigned interface.

It has come with its fair share of problems and even underwent its first "bug fix" recently. Even afterwards several users have taken to the Internet, MacRumors forums in particular, to voice their frustration and search for fixes.

"We are aware of an issue that affects a fraction of a percent of our iMessage users, and we will have a fix available in an upcoming software update," Apple said in a statement. "In the meantime, we encourage any users having problems to reference our troubleshooting documents or contact AppleCare to help resolve their issue. We apologize for any inconvenience this causes impacted users."

One of the most common and easy fixes for the iMessage problem is to reset the phone's network settings (go to settings, general reset, then click reset network settings). Some of those who have posted on the MacRumors forum have acknowledged other solutions like disabling iMessage and restarting the phone. While these serve as temporary fixes, they do not seem to last very long.

The iOS was released Sept. 18 to generally positive reviews, but since, more and more problems began to surface. For example, NBC News reported that iOS 7 users were very pleased with the settings control center, the new Safari and how the interface looks.

In an NBC online poll of more than 3,000 respondents, asking the favorite feature of iOS 7, 32 percent answered control center. The second most popular answer was "don't like it at all; bring back iOS 6" at 31 percent, followed by the "look and feel of iOS 7," at 30 percent. Improvements to Siri and the new photo filters received four and two percent of votes, respectively.

A study from UserTesting.com aligns with this very small poll, stating the control center is the most popular new iOS 7 feature by far.

"Most were generally happy with iOS 7 features with scores running above average," Jennifer Moebius of UserTesting.com told NBC News. "However, Spotlight (internal search) and Multi-Tasking received the lowest scores of 73 percent and 75 percent respectively. The Control Center received the highest score of 96 percent."

Also the subject of many complaints is the battery life. Plenty of new features like automatic app upgrade downloads, moving backgrounds and others cause battery life to disappear quickly.

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