Files from a client are backed up over the internet onto a back-up storage area. The client gathers identifying information for each file, including file size and file checksum. A client server estimates whether the information matches that present in a database including identifying information from multiple clients. When the information for a given file is present, the matched information is stored in the back-up storage area. When the information is not present, the given file is received from the client computer. The given file and the associated identifying information then are stored in the back-up storage area. The backed-up files are accessible in online storage, and may be archived. The client accesses the backed-up files over the internet in a restore operation, or as a virtual hard disk, a virtual CD image or a virtual DVD image. The backed-up files are accessible offline on a CD or DVD.