Quick Minecraft question

[ajh93]

i recently was given a friends Minecraft account and downloaded the game (the full version,no skin or texture mods yet) to my computer,and every time i try to open the game it says "The publisher could not be verified.",and i have to click the "run" option.also,Minecraft sometimes crashes completely out of the blue (one time it was right after the blocks i was placing were invisible).is this a serious problem?is it being caused by the game,or my computer?can it be fixed?
any help is greatly appreciated!

~ajh

 

[EternalFacepalm]

Google.

Oh, and that's a standard warning, it's just telling you that it might be a virus or something. Click "trust publisher" and ignore it.