Logging Out
To protect your email messages, calendar, etc. you should always log
  out when you are finished using the Horde groupware applications. This is
  especially true if your web browser will be left running.  To log out,
  click on the
 Logout icon located in the Horde application navigation menu.
 Logout icon located in the Horde application navigation menu.
 
 
 
If your login session is idle for a long period of time, you may 
  encounter a session timeout which logs you out.  This is a security
  feature which may help protect you if you forget to log out.  However,
  you should not depend on this mechanism to log you out.  You should
  always log out when you are finished.
 
For extra security, especially when using public or shared machines,
 it is a good idea to exit your browser completely after you log out.