Security researchers have found a security flaw in Skype. The flaw found several properties of Skype that can track not only a users' locations over time, but also their P2P file activity. The researchers also found that "even when a user blocks callers or connects from behind a Network Address Translation (NAT), it does not prevent the privacy risk" said the researchers. The research concluded that a user can initiate a Skype call, block some packets and quickly terminate the call to obtain an unsuspecting person's IP address without alerting them with ringing or pop-up window. Users also don't have to be in the contact list and it can be done even if the user configures Skype to block calls from non-contacts.