Apple has approved an app on Mac App Store with a troublesome crypto-mining feature, according to reports.

Calendar 2, a popular alternative for Mac Calander, is available was for download on Apple’s official Mac  App Store that gave users a way to access its premium features for free by letting the mining code run.

The feature doesn’t seem to be entirely malicious, but users have complained that the speeds of machines slowed down after using it.

It is yet unclear that whether the feature slipped past Apple’s watchful eye or it was really approved by the company.

The feature, included in app’s new update rolled out last week, was design to generate a crypto-currency called Monero.

The premium features of the app could be previously unlocked by getting the full version, which costs $18 (£12.90).

The feature doesn’t seem to be entirely malicious, but users have complained that the speeds of machines slowed down after using it.

However, after last week’s update, the users were able to get some of those features for no cost by letting the crypto-mining code run.

Following the complaints of trouble, the software was has been removed from the official Mac Store.

Calander 2’s developer Qbix on its website claims that app has 757,714 users and it has been used around 93 million times in total.

Qbix founder Gregory Magarshak said two security bugs caused the feature to consume more processing power which results in slower computer speeds.

He said the miner would be completely removed from future versions of Calendar 2.

“We have decided to remove the miner in the app. The next version will remove the option to get free features via mining,” Magarshak told Ars Technica in an email exchange.

“Ultimately, even though we technically could have remedied the situation and continued on benefiting from the pretty large income such a miner generates, we took the above as a sign that we should get out of the mining business,” he added.

Apple did not respond Ars Technica’s request to comment on the matter.