Apple has said it is taking steps to remove a malicious program found in a number of applications used by owners of iPhones and iPads in China.
It is thought to be the first large-scale attack on Apple's App Store.
The American firm said hackers had embedded a malicious code into the apps by persuading developers to use a counterfeit version of the firm's own software.
The program called XcodeGhost allows hackers to collect data from devices.
The infected applications include many used by iPhone and iPad owners in China such as Tencent's hugely popular WeChat app, a music downloading app and an Uber-like car hailing app.
A spokeswoman said the apps had now been removed.
"We've removed the apps from the App Store that we know have been created with this counterfeit software," Apple spokeswoman Christine Monaghan said in an email.
"We are working with the developers to make sure they're using the proper version of Xcode to rebuild their apps."
Eid this month, login names and passwords for more than 225,000 Apple accounts were stolen by cyber-thieves in China.
It was uncovered by security firm Palo Alto Networks while investigating suspicious activity on many Apple devices. It found a malicious software family that targets unlocked iPhones.
The majority of people affected were in China.