The FBI managed to crack open the iPhone 5C used by San Bernardino gunman Syed Farook by paying a one-time fee to an unnamed group of hackers, according to a Washington Post report.

The report says the hackers defeated the device’s security by using a previously undiscovered flaw in the software. This flaw was used to create a hardware device that helped open the iPhone without triggering another security feature that erases all of its data after too many unsuccessful log-in attempts, the Post says.

While the hackers aren’t identified in the report, it does claim that at least one is considered to be a “gray hat,” a term which describes hackers who tread a fine line between ethical and unethical hacking.