USING AN NP-COMPLETE PROBLEM TO DETER MALICIOUS CLIENTS

Methods and systems for using a challenge-response problem to deter malicious clients are described. A denial of a first login request for logging into an account by a computing device is detected. A second login request for logging into the account is received from the computing device. A reputation score for the second login request is determined based on the denial of the first login request. A number of terms for a challenge-response problem is set based on the determined reputation score. The challenge-response problem is configured to use the set number of terms and sent to the computing device. The second login request is authorized in response to verifying a second login credential and a solution to the challenge-response problem received from the computing device.