A Dutch team of hackers that calls itself “Doulci” claims to be the first group ever to hack Apple’s iCloud system. According to a report from Dutch news organization De Telegraaf, the hackers purchase stolen phones that have been locked for between $50 and $150 each. They then use a security vulnerability in order to access Apple’s iCloud system and unlock the phones, which are then sold for a large profit.

ValueWalk notes that the pair of hackers worked for five months to breach Apple’s iCloud system. The site also says that it tracked down a Twitter account that may be linked to the Doulci hacker group, highlighting a tweet in which an alleged hacker claims to have “processed” more than 5,700 Apple devices in just five minutes using the hack.

According to De Telegraaf’s report, the hackers first breached iCloud back in March and have since notified Apple, which has remained silent on the matter. The hackers say they finally decided to approach the Dutch media because Apple has not yet admitted publicly that its system has been compromised.

Apple did not issue a response to reports of the iCloud hacking, though De Telegraaf says Apple is working internally to address the issue.