What does an Intrusion Detection System (IDS) do?

An Intrusion Detection System (IDS) primarily functions to monitor network traffic for signs of unauthorized access or security breaches. This monitoring allows the IDS to analyze traffic patterns and detect any potentially malicious activities that could indicate an attempted intrusion into a network or system. By identifying these signs, an IDS can help network administrators to respond promptly to potential threats, ensuring enhanced security.

The other options do not accurately describe the functionality of an IDS. The prevention of all network traffic is not the role of an IDS; rather, it aims to identify and alert on suspicious activity while allowing legitimate traffic to flow. Creating secure user identifiers falls more within the scope of identity management systems instead of an IDS. Encrypting all data transfers is a function associated with encryption protocols and security measures rather than an IDS. Thus, the role of an IDS is distinct and focused solely on monitoring and detecting possible security breaches.