There is disclosed in one example a computing apparatus, including: a processor and a memory; a network interface to communicatively couple to a backup client; a storage to receive backup data from the client, including a plurality of versions and an associated reputation for each version, the associated reputation to indicate a probability that the version is valid; and instructions encoded within the memory to instruct the processor to: receive from the backup client a request to store a new version of the backup data; determine that the client has exceeded a backup threshold; identify a backup version having a lowest reputation for validity; and expunge the backup version having the lowest reputation for validity.