1. A method for use in a system with a server and one or more associated host computers (hosts), the method comprising: maintaining on a server for a plurality of files a set of server meta-information including, for each unique file content signature, a signature of the contents of the file, a date the file or the signature is first reported to the server, and state data indicating whether and with what conditions certain file operations can be performed by hosts on the file; maintaining on the hosts for a plurality of files a set of meta-information including, for each file the state data and the signature of the file contents; detecting on the host possible changes to file content or name, and updating host and/or server meta-information; and the server providing to the hosts changes in the server meta-information.