Question: What is the implication for a User Equipment (UE) when an Integrity Service Alert is issued with a 'Do Not Use' (DNU) flag set to false in E-UTRAN?
Option 1: The UE must discard all previously received assistance data.
Option 2: The UE is prohibited from using the corresponding assistance data for integrity computations.
Option 3: The alert has no impact on the UE's ability to compute integrity during that specified epoch time.
Option 4: The UE may use the corresponding assistance data for computing integrity, but only until the next epoch time.
Explanation: When an Integrity Service Alert is issued with a 'Do Not Use' (DNU) flag set to false, it indicates that the provided assistance data is suitable for integrity computations. However, since DNU flags are defined to be applicable only to the specified epoch time, the UE's permission to use this data for integrity purposes is limited to that timeframe, necessitating a potential reevaluation at the next epoch.