How do you buy the game Zombie Panic

Go to www.steamgames.com then type in Zombie Panic in the empty space or zombies... then you click where it says Zombie Panic, it's like a search system so it finds it then you click on it. Then it will give you a bit of information about Zombie Panic and there's a button that says download for free. BUT to get the game you must download steam. It's FREE also and very fast. You don't need to put any private information about yourself like name or address. Easy Peesy Lemon Squeezy!(If u have any questions about it ask me, I play the game EVERYDAY!)

ALSO< THE BAD NEW IS, that u must have Half Life the original version so u can get this!
This game is based on HL and HL costs 9 dollars or so. Sorry, but at least Zombie Panic is free if u already have Half Life.