Updates to the Source Engine have been released. The updates will be applied automatically when your Steam client is restarted. The specific changes include:

Source Engine

• Fixed a bug in networking that would cause long stalls (up to 10 seconds) when a split packet would not be reassembled properly, which forced a full update to all clients
  
• General optimization to tracelines
  
• Fix for broken .dem file playback
  
• Added backward compatibility code to allow demos recorded with protocol 12 to continue to be playable under protocol version 13
  
• When showing "WARNING: Connection Problem", now indicate the number of seconds remaining before an auto-disconnect will occur
  
• Fixed a bug that would cause NULLNAME to be shown as the player's name in the scoreboard for a short time