I have been a bit confused about the kind of password to use for my user accounts. There have been times during the course of registration for some website I have been prompted to use alphanumeric passwords while some other websites don't mind the kind of password combination I use be it purely alphabetic, numeric or alphanumeric. In fact, some registration forms require that your password contains symbols.
It is easier for me to remember a password written in alphabets or alphanumeric characters with one or two numbers but adding symbols makes it complicated and harder to remember. I read that alphanumeric passwords with symbols are very secure and difficult to decipher. How valid is this statement?