Currently any user can choose 123456 as a password, making their account more susceptible to hacking.
Many sites enforce the use of strong passwords, where password needs
1 - At least 8 characters long
2 - Contain at least one Uppercase letter
3 - Contain at least one Lower case letter
4 - Contain at least one Number
5 - Contain at least one symbol
Could also contain backwards compatibility for existing passwords, either to continue to allow them to work or force reset upon next login.
updated by @mysong: 10/31/14 10:06:54AM