How facebook is able to track all my friends

Does anyone know how facebook is able to track all my friends list? Many of my friends who were on my email account have now signed facebook and they told me that I invited them for free activation? How is that possible, I didnt invite them to join facebook? Also neither did I accept their friendship nor did I send them to add me on their friend list, but I was automatically added in their list? Is this some kind of hack used by facebook, are they playing with our piracy to make their website famous?

The reason being facebook is able to track all your friend is because, you might have used your email account in facebook to search for the contacts that are saved in your email account and after a search done by facebook, it might have automatically invited them to join facebook. After they registered on facebook, they might have probably added in your friend list.

I dont think that it is possible for anyone to get automatically added in your friend list. You either have to request a person whom who wanna join or add in your friend list on facebook or have to accept their request who wants to join you, nobody automatically gets added in each other's profile. However, there are some apps called "Places" which is used to track friends.

I have heard that facebook has enable members to track friends on other sites by using an application called Facebook Connect. It allows members to log onto other web sites using their Facebook login information and to see what their friends are doing on those sites. The company also believes that Connect, which is somewhat similar to separate ventures being trialled by Yahoo!, Google and MySpace.