1. A computer-implemented security method comprising: receiving, at a computer server subsystem and from a web server system, computer code that is requested to be served over the internet to multiple different computing clients; modifying the computer code in different manners for particular ones of the multiple different computing clients, so as to obscure operational design of the web server system that could be determined from the computer code; serving a first instance of the modified computer code to a first computing client among the multiple different computing clients; receiving an indication that the first computing client attempted to interact with an unmodified form of the computer code while executing the first instance of the modified computer code; and in response to receiving the indication that the first computing client attempted to interact with the unmodified form of the computer code, generating an indication that an abnormal event has occurred at the first computing client.