1. A system, comprising: one or more processors; and memory coupled to the one or more processors, wherein the memory comprises program instructions executable by the one or more processors to implement a backup manager configured to: attempt an input/output (I/O) operation with a live version of a data object; receive an I/O error code in response to the attempted I/O operation, wherein the I/O error code indicates that the live version of the data object is infected by malicious software; after receiving the I/O error code, compare a signature of the live version of the data object with respective signatures of one or more backup versions of the data object to identify at least one backup version of the data object; and store metadata in a backup catalog, wherein the metadata indicates that the identified at least one backup version of the data object is to be excluded from use during a subsequent restoration of the data object.