Solution for autonomously securing the use of a portable drive with a computer network. A data store is written and maintained that contains entries corresponding to a plurality of portable drives initialized for use with the computer network, each entry corresponding to at least one identifiable drive. Events are monitored as they occur on the computer network involving use of each of the plurality of portable drives. Predefined security policy determination criteria is applied, which can include drive mobility assessment criteria and drive content sensitivity criteria, to determine a drive-specific security policy for each one of the plurality of portable drives. A set of at least one policy enforcement action is executed that corresponds to a determined drive-specific security policy in response to detected usage activity for each one of the plurality of portable drives.