Information
The default TMOUT determines the shell timeout for users. The TMOUT value is measured in seconds.
Rationale:
Having no timeout value associated with a shell could allow an unauthorized user access to another user's shell session (e.g. user walks away from their computer and doesn't lock the screen). Setting a timeout value at least reduces the risk of this happening.
Solution
Edit the /etc/bashrc and /etc/profile files (and the appropriate files for any other shell supported on your system) and add or edit any umask parameters as follows:
TMOUT=600