28.9 Security Loopholes
will first check in the present directory for the specified file. Should a user put an executable file in /tmp with a common name, e.g. "ls", typing "ls" when in /tmp will execute their command, /tmp/ls.
Some people advocate putting "." at the end of your PATH. That's not sufficient, especially if you're prone to typing mistakes, e.g. typing mroe instead of more will not be found in one of the system files, but a thoughtful cracker could have one lying in wait for you.