symbol for authentication required denotes that authentication is required.

Choosing a Good Password

Don't use your login name in any form (as-is, reversed, capitalized, doubled, etc.)
Don't use your first or last name in any form.
Don't use your spouse's or child's name.
Don't use other information easily obtained about you. (includes license plate, telephone numbers, SSN, name of the street you live in, etc.)
Don't use a password of all digits, or all of the same letter.
Don't use a word contained in English or foreign dictionaries. Electronic versions of dictionaries of the following are available for hackers to guess your password:

English, Dutch, French, Yiddish, Chinese, German, Italian, Spanish, Sweden, Danish, Japanese, Norwegian.
Don't use a password shorter than 6 characters.
Do use a password with mixed-case alphabets.
Do use a password with nonalphabetic characters eg. digits/punctuation.
Do use a password that is easy to remeber, so you don't have to write it down.
Do use a password that you can type in quickly.

A few tips to help you

Pu together an acronym that's special to you, like Notfsw! (None Of This Fancy Stuff Works!) or AU*PEGC (All Unix Programmers Eat Green Cheese)

Take two short words and combine them together with a special character eg. book+mug, OR robot!sux, OR robot4my

[1] David Curry : Improving the Security of Your Unix System, Technical Report, SRI International, Menlo Park, CA, 1990

[2] Simon Garfinkel and Gene Spafford : Practical Unix Security, O'Reilly & Associates, Inc., Sebastopol, CA, 1993