Abstract: The present invention relates generally to security measures for protecting information on a network and more particularly to detecting falsifications made in the contents of websites on the Internet. In an embodiment of the present invention a method of detecting the falsification of contents of a plurality of files is provided. The method includes producing first falsification-detecting information corresponding to current filenames or current contents of the plurality of files; and detecting the falsification of the contents of the plurality of files by comparing second falsification-detecting information corresponding to the filenames or contents of the plurality of files at the time of registration or renewal with the first falsification-detecting information.

Abstract: This invention provides a method for identifying a purchaser who purchased content from which an illegal copy was produced. A provider system encrypts a content purchased by the purchaser using a public key of a purchaser system and sends the encrypted content to the purchaser system. The purchaser system creates a digital signature of the content with the use of a private key of its own and embeds the created digital signature into the received content. When an illegal copy is found, the provider system verifies the digital signature, embedded in the illegal copy as a digital watermark, to identify the purchaser who purchased the content from which the illegal copy was produced.