how does Alexa toolbar work?

[fumnimda]

As i know about Alexa.com it gather statistics about site popularity from Alexa toolbar which is downloaded by people and installed on their own PCs.right?
this toolbar has a search box.
my question is this:
Do Alexa get people browsed sites just are searched on this search box or all of the directly entered site address is calculated to?
i mean is the Alexa toolbar like a spyware but just about browsing history or just report what is entered on its search box?

hope could explain my question well ;)

[eoinbronks]

A complimentary software service that helps users becomes pros at surfing the Web. The service helps users establish the comparative value of web sites they stay through a variety of stats and details about each site and then recommends links of where they force want to go subsequently.

[localinternet]

Alexa toolbar is not working as spyware , it is not keeping an eye on visitor .it maintains history of visited webpage urls.if you visits a website more then one in a day then it will count only once.

[mackone]

Whenever you visit a site with Alexa Toolbar installed browser, you are giving an up rank for that website.