Updates to Left 4 Dead 2 have been released. The updates will be applied automatically when your Steam client is restarted. The major changes include:

Left 4 Dead 2
Added additional protection for critical files
All add-on files will be loaded when connecting to a Non-Official server regardless of game mode
Only approved custom maps will be loaded when connecting to an Official server
Player's can print the contents of the consistency list with "cl_print_consistency_list". If the server has sv_consistency disabled, the user will be notified when they attempt to print the list
Improvement to Hammer load times
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