In a data loss prevention system, what action involves preventing all access to original files while notifying the user?

In a data loss prevention (DLP) system, the action that involves preventing all access to original files while notifying the user is known as "quarantine." When files are quarantined, they are isolated from users, effectively blocking access to them to prevent any potential data breaches or leaks. This is crucial in maintaining data integrity and security, as it acts as a preventative measure until the file can be reviewed, assessed, and deemed safe for access again.

The process of quarantining not only restricts access but also typically generates a notification for the user, informing them that their access to certain files has been limited due to a potential risk identified by the DLP system. This dual action of blocking access and providing notification helps ensure users are aware of security measures being enforced without compromising the data.

In contrast, the other options reflect different actions involving data management and user notifications. "Block" refers merely to stopping access without the notification aspect, "alert" pertains to informing the user about a potential issue without restricting access, and "tombstone" generally refers to marking an entry as inactive without directly managing access to files.