Question: What security measure is primarily used to prevent unauthorized access to an IOPS (IOPS Network or a normal Public Land Mobile Network - PLMN) due to malicious switching of USIM applications?
Option 1: Enhanced Encryption for Backhaul Links
Option 2: Use of Distinct Security Credentials for Each Application
Option 3: Mandatory Authentication of eNBs in IOPS Mode
Option 4: Regular Security Audits on Local EPCs
Explanation: The correct answer, "Use of Distinct Security Credentials for Each Application", highlights a key security strategy. By utilizing a distinct set of security credentials for each USIM application, the risk of unauthorized access to either an IOPS network or a standard PLMN (Public Land Mobile Network) due to malicious switching between these applications is effectively mitigated. This approach ensures that even if an attacker manages to switch between applications, they won't have the necessary credentials to access sensitive networks, thereby protecting both the network and user data.