SYRACUSE, N.Y. -- Chris Roberts sent out a tweet Wednesday aboard a jet headed to Syracuse, joking about playing around with the in-flight communications system.

The feds were not amused.

Two FBI agents and two Syracuse police officers pulled Roberts from the United Airlines flight when it landed and questioned him for four hours, according to a report in Forbes.

Roberts is a cybersecurity expert who had flown from Denver to Chicago to Syracuse to speak at an aerospace conference about vulnerabilities in airplane systems, according to Fox News.

Roberts wasn't charged with a crime and was eventually allowed to go on his way. FBI agents in Syracuse and Denver refused to comment. Syracuse police also would not comment.

Here's the tweet that drew the FBI's attention:

Find myself on a 737/800, lets see Box-IFE-ICE-SATCOM, ? Shall we start playing with EICAS messages? "PASS OXYGEN ON" Anyone ? :) — 42... (@Sidragon1) April 15, 2015

After the agents questioned Roberts for four hours, he refused to hand over his electronic equipment, he told Forbes. The agents seized all but his phone, including an iPad, a MacBook Pro, three hard drives, a flash drive and USB sticks, according to Forbes.

Roberts tweeted:

Lesson from this evening, don't mention planes....the Feds ARE listening, nice crew in Syracuse, left there naked of electronics — 42... (@Sidragon1) April 16, 2015

The next day, Roberts wrote this and included a picture of his seized property:

Bye bye electronics, all encrypted....and all now in custody/seized pic.twitter.com/a5o6rYTbZ0 — 42... (@Sidragon1) April 16, 2015

He had this message for United:

Hahaha!! Well United, let me tell you about my trip and the new friends I made :-)) pic.twitter.com/RUVo8Nlsdu — 42... (@Sidragon1) April 16, 2015

His tweets today:

Eating breakfast inside the airport, so far no alarms, no klaxons, can almost taste the freedom of flight.... No electronics either though.. — 42... (@Sidragon1) April 17, 2015

Ok made it TO plane in Syracuse...now let's see what happens :-) still NO warrant, and no electronics..... pic.twitter.com/TX5aKxLO97 — 42... (@Sidragon1) April 17, 2015

He sent this tweet after getting back to Denver shortly after noon:

It's cloudy, soggy and snowy but I made it back to CO!! :-) no sign of suited gate agents thankfully!! — 42... (@Sidragon1) April 17, 2015

Roberts told Fox last month that commercial planes have a weak spot in their entertainment and satellite communications systems that could leave them vulnerable to hackers or terrorist attacks.

"We can still take planes out of the sky thanks to the flaws in the in-flight entertainment systems," Roberts told Fox. "Quite simply put, we can theorize on how to turn the engines off at 35,000 feet and not have any of those damn flashing lights go off in the cockpit."

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