1. A computer implemented method comprising: maintaining user profiles for a plurality of users of a social networking system; maintaining a plurality of connections between the users of the social networking system; receiving a request from a requestor for access to a computing resource, wherein the request is associated with a user of the social networking system; selecting, for forming a challenge question, another user of the social networking system from a plurality of other users connected to the user via the social networking system, the selection based on a rate of interactions between the user and the other user; obtaining information from a user profile of the other user; determining whether the request is received from a suspicious source; determining difficulty level of the challenge question based on whether the source is suspicious; forming the challenge question according to the determined difficulty level, by a processor, wherein an answer to the challenge question comprises information obtained from the user profile of the other user; sending the challenge question to the requestor; and responsive to receiving a correct answer to the challenge question, allowing the requested access.
1. A computer implemented method comprising: maintaining user profiles for a plurality of users of a social networking system; maintaining a plurality of connections between the users of the social networking system; receiving a request from a requestor for access to a computing resource, wherein the request is associated with a user of the social networking system; selecting, for forming a challenge question, another user of the social networking system from a plurality of other users connected to the user via the social networking system, the selection based on a rate of interactions between the user and the other user; obtaining information from a user profile of the other user; determining whether the request is received from a suspicious source; determining difficulty level of the challenge question based on whether the source is suspicious; forming the challenge question according to the determined difficulty level, by a processor, wherein an answer to the challenge question comprises information obtained from the user profile of the other user; sending the challenge question to the requestor; and responsive to receiving a correct answer to the challenge question, allowing the requested access. 6. The method of claim 1 , wherein the request is a request to login to the user's account.