Preventing phishing attacks based on reputation of user locations

User sessions are authenticated based on locations associated with a user account used for sending a request for creating a session. Examples of locations of a source of a request include a geographical location, a network address, or a machine cookie associated with a device sending the request. Locations of the request are compared with stored safe locations associated with the user account and a suspiciousness index is determined for the session. The level of authentication required for the session is determined based on the suspiciousness index. Locations are associated with a reputation based on past history of sessions originating from the locations. A location associated with a history of creating suspicious session is considered an unsafe location. Reputation of the location originating the session is used to determine the level of authentication required for the session.