The news organization Quartz, which has been covering the Hong Kong protests in depth, recently found its app unavailable from Apple's app store in China.

Quartz received a notice from Apple on September 30 that said the app was being removed "because it includes content that is illegal in China," according to a Quartz spokeswoman. No specifics were given on what that content was, she said.

The news outlet also said that its entire website is inaccessible in mainland China.

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Quartz has been covering the protests in Hong Kong for months, including information on how readers can get around government censorship by using VPNs, or virtual private networks.

"We abhor this kind of government censorship of the internet," Zach Seward, Quartz's CEO, said in a statement.

Apple did not immediately reply to CBS News' request for details on what content was deemed illegal.

The company has also pulled an app used in the Hong Kong protests, HKmap.live, from its China app store. The app disappeared Wednesday night after a government-backed Chinese newspaper accused it of facilitating illegal behavior.

Apple's decision to remove the app has been met with harsh criticism. But Apple CEO Tim Cook defended the decision Thursday in an email distributed to company employees, according to The Verge.

Cook said in the email (first published by HKmap.live's developers) that the app's information, including mapping of police checkpoints and protest hotspots, was "benign."

However, he said, Apple had received "credible" information from Hong Kong law enforcement authorities in recent days that "the app was being used maliciously to target individual officers for violence and to victimize individuals and property where no police are present."

That violates Apple policies, Cook continued: "This use put the app in violation of Hong Kong law. Similarly, widespread abuse clearly violates our App Store guidelines barring personal harm."