User accounts are the way that computers keep information separate and keep track of who did what. Your user account can be used as a way to determine if you did or did not do something.

In most cases today the password is the part that keeps your user account to be used only by you. There are some additional techniques being implemented now that not only use passwords but use other things like identification of your face or eye or fingerprint or asking random unique questions about you that you previously supplied answers to.

Most people would agree that sharing their ATM or debit card code is not a responsible action as that information could be used to drain your bank accounts. Of course for many people (particularly my students remind me when they give me their social security number instead of student ID) that if you have no money then there is no money to drain.

However people will share their password to get on the computer systems at their office or where there are shared objects that others can them put stuff like for instance Dropbox. That may sound simple but can cause problems. First is that most people try to only use one or two passwords so if you give me your password to Dropbox I may now know your password to your Discover card or bank account (and since I know you, I may well know answers to the questions in two step process.

Dropbox and many other internet sites like it allow you to upload and share files. It is relatively simple to set up an account for each person to use it. Then when they put files in there they show who shared the files. If just allow everyone to use the same account to share files they will all show from that one account which may have be Jane's account. If Dick uses Jane's account also it shows what Dick did as being done by Jane. What happens when Dick decides to share some inappropriate pictures in there (for Sue and John) and the law or their boss discovers these inappropriate pictures? Jane is in trouble as they all show they were uploaded by her. Likewise if Dick uploads work he did and says he did it, the program shows it was done by Jane.

Keep your passwords private. There is very rarely that case where you do need to allow someone else use of your password to accomplish some task but it should be extremely rare and the first thing you should do after having done that is change your password so it is all secure again.