On a Somali flight (Daallo Airlines Flight 159). A laptop full of explosives was smuggled aboard a flight and detonated against the airplane's hull, blowing a hole in it. The only fatality was the bomber, who was sucked out the hole.
The issue was that, in order to get this laptop around checked bag security in Mogadishu (which isn't too good, but enough so that the terrorists didn't risk carrying it through), they had to have an airport employee carry it in and hand it to the passenger. Now if this is what the USA and GB are worried about, we have a really big problem. If an airport employee can sneak in a laptop, they can sneak in anything up to the allowed carry-on size. It doesn't have to be electronics. It could be a hollowed out bible or koran. The only way to protect against this kind of threat would be to shut down all flights originating at or passing through an airport suspected of being compromised.