6. The messaging system of claim 1 , wherein the database comprises a plurality of replacement text elements, each of said plurality of replacement text elements corresponding to one of the plurality of permitted words.
1. A computer network-based messaging system for controlling content of messages sent by users in the messaging system, the messaging system comprising: an electronic data storage device containing a database including a plurality of permitted words and at least one replacement text element corresponding to at least one of said plurality of permitted words; a message filter that receives an entered word or phrase input by a user on a messaging device as part of a message, wherein the message filter uses a processor to replace the entered word in the message with a replacement text element stored in the database that matches the entered word, wherein the replacement text element includes an excluded word that is not a permitted word included in the database; and a message sending part that transmits the message including the replacement text element over a data network for viewing by at least one other user only if every word in the message is: a permitted word included in the database, and/or a word that forms part or all of a replacement text element included in the database, wherein the message sending part transmits the message including the replacement text element even though the replacement text element includes the excluded word, where the message sending part would not transmit the message if the same excluded word had been received as part of the entered word or phrase input by the user.