A 34-year-old man has been accused of paying AT&T employees thousands of dollars over the course of five years to unlock millions of phones tied to the company’s network. The Department of Justice says that Muhammad Fahd, who has been extradited to the US from Hong Kong, paid one employee over $420,000 over five years to unlock the phones.

Initially, the DOJ says that Fahd would simply provide the AT&T insiders with phone International Mobile Equipment Identity (IMEI) numbers, and they would use the company’s internal systems to unlock these devices. However, after all but one of his contacts were fired by the company, Fahd worked with his remaining co-conspirator to install malware that would allow him to unlock the phones remotely. Forbes notes that Fahd even paid employees to install compromised routers and Wi-Fi access points so that he could gain further entry into the company’s computer systems.

Fahd faces up to 20 years in prison if found guilty

The DOJ estimates that, in total, his actions cost AT&T millions of dollars in lost revenue as phones were transferred off its network. Forbes reports that Fahd would take payments from customers who were looking to unlock their phones and leave AT&T’s network. He would make payments to his AT&T contacts via a series of front companies after initially approaching them over Facebook Messenger or via a telephone call. Three of these insiders have already pleaded guilty to being paid to participate in the scheme.

If found guilty, Fahd faces up to 20 years in prison for a litany of charges, including several counts of wire fraud and conspiracy to violate the Computer Fraud and Abuse Act. A co-conspirator, Ghulam Jiwani, who allegedly gathered the IMEI numbers and paid the bribes, is believed to have died in the years since the alleged fraud occurred.