Apps that promise to spy on people, or allow the user to interact with other Facebook users in ways that the social network does not allow, are illicit and very likely a scam, Bitdefender said. While the app may be freely available, victims are prompted with quizzes and surveys and the data collected is used in aggressive advertising. In a recent study, Bitdefender estimated that more than 30 percent of suspicious apps attempt to provide additional services such as traffic profiling to determine who is viewing your profile, who deleted your connection and who is a "profile stalker." While some services may be legit, many of them use the access granted to view Facebook connections and collect other information that may be considered personal, the security firm said.