The present invention provides a method and system for securely transferring data over a computer network. A first party's computer: parses vulnerable words and numbers of a data set providing information for a second party, generates masked values of the parsed vulnerable words and numbers, updates the data set by replacing the vulnerable words and numbers with the masked values, and sends the updated data set to a third party for analysis, and for subsequent decoding, by the second party, of the masked values of the parsed vulnerable words and numbers. The first party's computer generates a first, second, third and fourth symbol of the masked values of a parsed word by: incrementing a first symbol of the parsed word by one, decrementing a second symbol of the parsed word by one, decrementing a second symbol of the parsed word by one, and inserting a predetermined marker symbol, respectively.