EgyptAir flight MS804 from Paris to Cairo disappears from radar

Disappearing at that altitude, without somebody disabling the transponder, indicates an explosive decompression. These days, that typically only happens with a bomb or a missile.

In the older days, structural failure was a common cause (a blown cargo door UA811, the roof coming off Aloha 243). That just doesn't happen anymore.

Another possibility is a hijacking. Another EgyptAir flight was recently hijacked by a man wearing a vest containing fake explosives. The plane landed safely. Some dude took a selfie with the hijacker.

A Russian airliner recently exploded over Egypt as well.

Link appears to be broken. This is the correct one: http://www.bbc.com/news/world-middle-east-36309492