The Node.js event loop can be used as a side-channel for timing attacks, allowing attackers to exploit vulnerabilities in authentication mechanisms. The challenge "Sequence Hunt" involved solving an algorithm that took varying amounts of time to execute based on the input values, making it susceptible to timing attacks. The server's implementation was designed to prevent such attacks by waiting at least 3 seconds before responding to each request. However, the event loop provided a way for attackers to measure the execution time of the algorithm by sending multiple requests concurrently and measuring the time differences between them. By exploiting this vulnerability, an attacker could determine the correct input values that would result in the shortest execution time, allowing them to break into the system. To prevent similar vulnerabilities, it is recommended to use constant-time comparisons for authentication checks and to regularly check for known vulnerabilities in the codebase.