Game trying to download files from internet

[76561198145944317]

So, I have an old friend (which is not my friend) I think we once played and I added him. He usually plays left 4 dead but neven with me. So, today he invites me to play and I click to join his match or lobby and I get a message from left 4 dead.

The message was something like "do you want to download this expansion map? Downloading these files have the same risks as if you download them from internet, might contain viruses or unwanted files". I obviously declined and click on back.
My question is, is this normal? if so, why valve allows the game to download files from unkown sources? this message shouldnt even show because valve shouldnt allow it.

Any thoughts about this? thanks!

[Zombie Tsunami]

It is normal. If the link goes to l4dmaps, gamemaps.com or the steam workshop you should be ok.

[76561198145944317]

Originally posted by Thurston Howell III:

It is normal. If the link goes to l4dmaps, {LINK REMOVED}gamemaps.com or the steam workshop you should be ok.

I couldnt know since I click "back" :P , but is normal you say

[Zombie Tsunami]

Originally posted by broly:

Originally posted by Thurston Howell III:

It is normal. If the link goes to l4dmaps, gamemaps.com or the steam workshop you should be ok.

I couldnt know since I click "back" :P , but is normal that the game tries to download games from another site?

Yes.

[Red Eclipse]

Yeah this is normal. He's probably trying to invite you to a custom map you don't have yet. The game was simply trying to download and install the map so you could play together.