CounterStrikeee

[MiStAHxMuRkA]

lolololololol

[drawnzer54]

Simply change the password through the Steam Community which pops up on opening of Steam.

If you can't find it try going to Steams official website and change your password.

[Kn7ghT]

If he has your password, he can change every aspect of your account, email, security question, with a couple clicks.

[FabianN]

It's stupid to share a steam account with anyone but direct family members. Change the password and tell him to buy his own copy.

[Sashimi]

I'm sharing one of my spare accounts with a friend. He won't hack it cuz I can trust him.

[FabianN]

No, like im trying to find a back up plan. If he really DOES hack my acount what can i do to get it back? Will sending my cd key and information to steam work?

There are methods, but they take time and are not guaranteeble. Mostly you need to be able to prove that you were the one that purchased the games. If you bought via steam, having the credit card information used to purchase games.
But in the end there is no safe way to secure your account if you just gave you password out like that.

[Deimos]

some people i just really dont understand. why would you share in the first place if you dont trust him?

It's stupid to share a steam account with anyone but direct family members. Change the password and tell him to buy his own copy.