In call of duty PC mutiplayer it won't let me join games because of my PK3 file is wrong. plz help me. (i'm not a computer genius)

this is what it said:
Unpure client detected. Invalid .PK3 files referenced!
C:\PROGRA~1\CALLOF~1\main\___CoDaM_HamGoodies__CoD1.1__.c5aae451.pk3

basically what it is saying is that the PK3 file is not the correct file. It has been modified.

Typically seen in Pirated copies of the game.

Is this a legit copy or a pirated one.. if it is legit uninstall the software compeletely and reinstall it.

thanks man.