Due to recent advances in wireless communication technologies, mobile ad hoc networks (MANETs) have become the networks of choice for use in various applications. Unfortunately, this advantage comes with serious security concerns, particularly from a wireless channel prospective, where MANETs may be vulnerable to collaborative wormhole attacks, in particular, packet dropping and message tampering attacks. Recently, two secured routing protocols against these types of attacks (the so-called Highly Secured Approach Method or HSAM and the so-called Securing AODV against Wormhole Attacks in emergency MANET Multimedia Communications or AODV-WADR-AES) were proposed. These schemes are investigated in-depth to identify their weaknesses and a novel secured routing scheme (so-called Timed and Secure Monitoring Implementation against Wormhole Attacks in MANETs or TSMI) is proposed, with the goal to mitigate collaborative wormhole attacks in MANETs while maintaining the performance levels of both the HSAM and AODVWADR- AES schemes. Simulation results are presented to validate the stated goal using various performance metrics.