SAN FRANCISCO — A computer security expert hacked into a plane's in-flight entertainment system and made it briefly fly sideways by telling one of the engines to go into climb mode.

Chris Roberts of One World Labs in Denver was flying on the plane at the time it turned sideways, according to an FBI search warrant filed in April.

The warrant was first publicized on Friday by APTN, a Canadian News Service.

Roberts told the FBI he had hacked into planes "15 to 20 times," according to court documents first made public Friday.

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Roberts first made news in April when he was told he couldn't fly on United Airlines because of tweets he had made about whether he could hack into the flight's onboard computer settings.

The FBI search warrant describes him doing just that.

According to the document, in an interview on Feb. 13, 2015, Roberts told agents he had hacked into in-flight entertainment centers on Boeing 737s, 757s and Airbus A-320 aircraft "15 to 20 times."

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The warrant describes how Roberts would wiggle and squeeze the Seat Electronic Box under his seat, which connected to the plane's in-flight entertainment system, or IFE.

He would then connect a cable to the box and connect it to his computer. From there, Roberts was able to hack into the plane's IFE system using default IDs and passwords.

He overwrote computer code for the planes' thrust management computer, which he told agents allowed him to make the plane climb on his command.

At least once, according to the document, he told one engine on a plane to climb, causing the plane to move sideways as it flew.

Roberts also used software to monitor traffic from the cockpit, according to the search warrant request.

Roberts is a well-known and respected expert on computer security. He told the FBI he was furnishing the information "because he would like the vulnerabilities fixed."