A security device may receive a request from an attacker device and intended for a server device. The security device may identify the request as being associated with a malicious activity. The malicious activity may include one or more undesirable tasks directed to the server device. The security device may generate an unsolvable challenge-response test based on identifying the request as being associated with the malicious activity. The unsolvable challenge-response test may be generated using at least one construction technique and may be configured in an attempt to block the attacker device without making the attacker device aware that the attacker device is being blocked. The security device may provide the unsolvable challenge-response test to the attacker device, and may receive a solution associated with the unsolvable challenge-response test. The security device may notify the attacker device that the solution is incorrect regardless of whether the solution is actually correct.