They are confirmed by hackers but not Nintendo itself. It seems to be real since Showdown has put their Megas under the "unreleased" tab.
They're real they just haven't been officially released yet.
Since they're not officially released nothing is known about them however their Stats are rumoured to be:
Mega Latios: 80/130/100/160/120/110
Mega Latias: 80/100/120/140/150/110
http://pokemondatabase.psim.us/ (!data Mega Latios) (!data Mega Latias)
Hope I helped :)