According to the FBI document, which was first made public by the Canadian news website APTN, Roberts was able to hack into the onboard entertainment systems — manufactured by companies such as Panasonic and Thales — of passenger planes such as the Boeing 737, the Boeing 757 and the Airbus A320. He did so a total of 15 to 20 times between 2011 and 2014. To do so, he hooked his laptop up to the Seat Electronic Box (SEB) — which are usually located under each passenger seat — using an Ethernet cable, which is unsettling enough.

But Roberts may also potentially have used the SEB to hack into sensitive systems that control the engines. In one case, he may even have been able to manipulate the engines during flight. He says that he was able to successfully enter the command “CLB,” which stands for “climb,” and the plane’s engines reacted accordingly, he told the FBI, according to the document.

Roberts is currently keeping a low public profile, taking to Twitter last week to say that his “legal team are still requesting I wait on saying anything.” He did, however, write that “over last five years my only interest has been to improve aircraft security.” He says that the FBI “incorrectly compressed” that work into a single paragraph in its affidavit.

The FBI, it would seem, is taking Roberts and his efforts to hack into airplane computer systems extremely seriously.