Facebook – How does the “Facebook profile visitor” application work

Facebook has access to all friendship-data on their site, even if you lock down the privacy settings. As an addition many users share their contact-book or even e-mails with Facebook. Most peoples have filled out their profile quite decent so it has data about your school, your employer, your current place, your interests and so on. Although Facebook states it does not use it, they can track all users (and even non-users) across many websites via the "like"-button which is transcluded directly from Facebook.

From this data it can calculate this friend requests.

No.

Taken from Facebook's FAQ:

Facebook does not provide applications or groups with the technical means to allow people to track profile views or see statistics on how often a particular piece of content has been viewed and by whom. If an application claims to provide this functionality, please report the application by going to the application’s About page and clicking "Report Application" at the bottom of the page, or by clicking "Report" at the bottom of any canvas page within the application.

Applications you use may ask for permission to access content from your News Feed and Wall. Granting this permission does not allow applications to see who has viewed your profile. It simply allows applications to see which friends have interacted with posts, such as which friends liked or engaged with a particular wall post.

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