Programs Which Interfere with Steam

http://support.steampowered.com/cgi-bin/steampowered.cfg/php/enduser/std_adp.php?p_faqid=451

Run the Steam Background Applications Test

steam://support/?Issues=Background*

Review Installed Applications and Running Processes

Any applications running in the background will affect gameplay and video performance. The applications listed below are known to generate connection errors or crashes, however, it is recommended that you close all background applications when playing through Steam to ensure the best performance.

Please see the Disabling Background Applications article if you would like instructions to prevent background applications from loading when Windows starts.

Issues related to any of the programs listed below may be resolved by exiting the program and then exiting and restarting Steam.

• Antivirus Software
  Incorrectly-configured antivirus software may prevent proper operation of Steam and Steam games. VIGuard antivirus software has been found to conflict with Steam games - an error message stating "Failed to duplicate pipe handle" will be generated when attempting to load the game. Add the contents of your Steam installation folder to VIGuard's authorized folder exceptions list to correct this issue.
• Spyware Detection Software
  Steam is not spyware, however, aggressive spyware detection software may block the normal operation of Steam. We have received reports that Spycatcher Express may prevent Steam client application updates.
• Peer-to-Peer (P2P)
  P2P programs such as Kazaa, LimeWire, BitTorrent, E-mule, and Exeem can consume a large portion of your bandwidth, which may prevent Steam from connecting.
• FTP and Web Server Applications
  As with P2P programs, these programs are generally very bandwidth-intensive and may generate errors in Steam.
• IP Filtering Programs
  Peer Guardian, CYBERsitter, and Netlimiter have been found to cause Steam connection issues.
• IP Masking Programs
  Programs designed to mask your IP (GhostSurf 2008, Anonymizer, etc) will impact Steam's ability to send and receive data.
• Windows Theme Editors
  Tuneup WinStyler Theme Service has been found to cause a crash with the Steam client application and WindowBlinds may cause crashes with Source games.
• Virtual Private Network (VPN) Software
  VPN software will prevent the Steam client application from accessing the Steam network.
• Other Programs
  • Look'n'Stop has been reported to cause issues with Steam when its "Unknown UDP Packet" filter is enabled.
  • PowerStrip custom display modes software may cause issues with load time and crashing in games - it is recommended that you select the "Restore to default" setting in PowerStrip before playing (you may resume using PowerStrip normally once you are done).