iOS 7 nabs more than 50 percent of Apple users in first week

It's been a little more than a week since Apple released iOS 7, and the new OS has quickly blown past its predecessor. At least in some parts of the world.

That's according to advertising network Chitika, which on Wednesday said iOS 7 is now found on 51.8 percent of iOS devices in North America. That's up sharply from the 18 percent the firm estimated were using it just a day after the software came out.

Chitika's data comes from a sample of "tens of millions" online ad impressions in North America from more than 300,000 Web sites. That means those metrics aren't necessarily indicative of global iOS adoption.

By comparison, Apple on Monday said that more than 200 million devices were running iOS 7, nearly a third of the iOS devices the company has sold so far, and faster than any previous iOS launch. The exact total of iOS devices is unclear at the moment, with Apple only saying last week that it anticipated selling its 700 millionth iOS device sometime in October.

iOS 7 brings a number of new features to the iPhone, iPad, and latest iPod Touch, though mainly a visual revamp of every single built-in application, as well as elements such as the lock screen. Like previous releases, the software is not available on some older devices, which include iPhones prior to the iPhone 4, iPods before the fifth-generation iPod Touch, or the original iPad.

The number of users running Apple's latest software has become a bragging right for the company, which in June noted that iOS 6 was installed on 93 percent of its then 600 million devices. Beyond the user-facing features, each major release has included new APIs for developers, who have to balance compatibility with older devices against including the latest software features.

Update at 1:42 p.m. PT: Also worth noting is an iOS adoption tracker from Mixpanel, which currently has iOS 7 at 61.31 percent of all iOS devices, compared to iOS 6's 35.35 percent share. Thanks Jim!