How do they KNOW MY ID?

[GeminEye2k5]

this is a newbie question probably but I was wondering if it is illegal for someone online within a game to be able to KNOW my STEAM USER ID somehow....I was recently playing on a NETSPEED server and some of the players new my login....how is that POSSIBLE?.....they didn't know my password thank god...but they new my ID....I searched online and found out how to find the actual #ID....easily by typing STATUS within a game online....but this player new my Name that would appear on the friends list....weird huh?....or is it normal?....thanks for any help.....:thumbs:

 

[joule]

Menu->Player List->Voilà!

 

[_Z_Ryuken]

QFR.
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[GeminEye2k5]

thanks for the help.....lol....simple.....but I have a another question....How do you change your name within the game using cool symbols and characters????....i've seen a bunch of players with those types of names...I want one too....thanks for the help......:thumbs: