Google Plus Circles Venn Diagrams

Circle is a very common word of usage to describe a specific set of people a person is to connected to in some way. It is a very nice easy adapt word used for categorizing friends on google plus. Though the name says circles and UI has a few circles for adding friends to on google plus, it does not fully exploit the advantage of using circles for such concept. Circles have special properties both mathematically, socially and philosophically. Some of the changes which can enhance the usability of circles are as follows

• Use a venn Diagram which in turn can
• take the advantage of intersections, unions and exclusions to categorize people into multiple categories in one step rather than having to add one person to multiple circles
• human mind can process this kind of visual data better
• The size of the circle can be proportional to the number of people added to it
• If a specialised dot can represent oneself, then the distance of this dot to other other people in a circle can decrease as the communication, likes between them increase. But all the dots are restricted to move with in their own circles.

facebook password history

How much password history is facebook storing. I entered an old password by mistake, Facebook gives me the following information along with a login failure message

• the password entered is an old password.
• The date and time when it was changed.
• the computer and the network from which the password was changed is also suggested vaguely

This can be a  potential hit and try hack to gain access. The old password on facebook can be active on some other accounts that the user uses.

Why does facebook need to store password history at all