Modern passwords are made of characters, letters and numbers. Sometimes a password will require a minimum number of characters. Usually this is from six to eight. Some websites allow only the use of letters and numbers, but no other characters on the keyboard. Other websites advise using a combination of letters and numbers to increase the "strength" of a password. Websites also advise changing a password once a year or more often to prevent hacking. A person may be able to guess a password if it is too easy. While being typed, each letter of a password is shown as * or •. 