The tainted version of Xcode was downloaded from a server in China that developers may have used as it allowed for faster downloads than Apple’s U.S. servers, Mr Olson said.

Cyber security firm Palo Alto Networks Inc, reported that Chinese iOS developers revealed the new OS X and iOS malware on microblogging service Sina Weibo.

The Apple App Store suffered a malware attack on Sunday when it was found that hackers had copied and changed some of the Xcode development software called XCodeGhost.

The incident is the only the sixth time malicious software is known to have made it through Apple’s screening process for products on its App Store, according to Xiao.

Sources familiar with the matter said mainland developers had long complained about slow downloads of Xcode and other business tools because access was squeezed by China’s firewall, which blocks websites prohibited by online censors. Maybe these problems have been sorted out enough to get more people on board with the most up to date iOS software.

Apple reportedly said it had addressed the security breach and had teamed up with developers to help fix affected apps.

In a blog post, Cockerill said that “while Apple has traditionally done an excellent job of keeping malware out of its App Store, malicious actors are always looking for new ways to break through”.

One developer said that XcodeGhost had already launched phishing attacks aimed at acquiring users’ iCloud passwords, Palo Alto Networks noted.

According to Apple, malicious hackers have found a way to infect the App store with malicious code that could impact iPhones and iPads.

“Since the dialogue is a prompt from the running application, the victim may trust it and input a password without suspecting foul play”, Palo Alto Networks said in its blog post. A preliminary investigation showed there had been no data theft or leakage of user information, the company said.

This is a big security issue, because even though the number of apps affected by the malware may seem small compared to the total number of apps in the App Store, the number of users that could be affected by this malicious apps is huge.

Apple announced Monday that half of all Apple devices have upgraded to its latest mobile operating system in the past five days, the most rapid adoption of an iOS ever.