Hi. I have been playing dota 2 about 900 hours.
So one day, i was trying to play, after accepting the game Steam messaged me "Steam validation rejected"
I was googling this problem, tryied to find solution, (deleted registery.bob file from my steam folder, connected to my computer directly internet, restarted WIFI, and etc.) but nothing helped me.
I was trying my friends acc.
So after i connected and was trying to play dota 2, its worked perfectly.

Yestarday i messaged to Steam support, so they answered me "If you wish to report a bug with Dota 2 in-game items, skill behavior, balance issues, team configurations, or anything else, please do so in the official Dota 2 Developer forums. This will reach the Dota 2 developers much faster than a Steam Support ticket."

Sorry for my english.
Hope its fixable.