Some posters need to take a step back. There is absolutely a 0% (zero) chance this a/c entered Russian airspace.
Did you forget about the Cessna-172 which was flown unchallenged across former Soviet Air Defense Identification Zone from Helsinki to Moscow, and successfully landed in Red Square?
This was dated in 1987, one and half year before whole eastern block collided.
Today's Russia is different. Moreover with Russian/Ukrainian crisis ongoing, Russian military is on high level of alertness. And as you probably know, USAF are on air manoeuvres at Poland, close to Ukrainians borders (with AWACS) and Russia air force over Black sea. I would be highly sceptical to find out, that they missed target huge as 777, even if it was coming from not so exposed direction.