Apple has raised the possibility of using iPhones and iPads to perform transactions in bitcoin and other cryptocurrencies, after a change in the rules by which it approves software for its app store.

Until now, the company had gained a reputation for rejecting apps which enabled cryptocurrency transactions, generally citing rules which banned developers from submitting apps which break the law.

The new App Store review guidelines state that "apps may facilitate transmission of approved virtual currencies provided that they do so in compliance with all state and federal laws for the territories in which the app functions."

But the guidelines do not specify which virtual currencies are "approved", nor how one goes about getting approval from the company.

Apple did not immediately respond to an email from Reuters seeking more information.

An alternative possibility for the rule change is that the company is expressly allowing "currencies" like the coins used to buy upgrades in free-to-play games. Such payments are already widespread on the App Store, but have no specific rules enabling them.

In the past, Apple has been aggressive about removing apps from its store which enable bitcoin payments.

The Blockchain.info app, which flew under the radar for two years, was removed in February with little explanation given. In December 2013, a second app, secure messaging service Gliph, was forced to remove functionality for sending bitcoin payments with messages.

Only one developer has received an open answer from Apple as to why their app was removed. When BitPak was pulled from the app store in 2012, its developer Rob Sama said that "I asked [an Apple staff member] why this had happened, and he said: 'Because that Bitcoin thing is not legal in all jurisdictions for which BitPak is for sale'".

That requirement, rule 22.1 in the company's guidelines, is still present, but apparently superceded by the new rule about virtual currencies.

The change may have come too late for Apple to capitalise on the bitcoin boom, however. Spurred on by the company's repeated rejections of bitcoin apps, a number of developers have built bitcoin wallets that work in a user's web browser, negating the need for Apple's approval entirely.

Coinpunk, the most popular of these, was started by developer Kyle Drake in 2013, and funded by the Bitcoin Foundation thanks to its "ability to serve as a base for a wide range of innovations in keeping with open source ideals."

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