India, Feb. 20 -- Yahoo! - and to a lesser extent Hotmail - were the kings of the internet, in the late-1990s. Their free webmail services gave anyone with a modem a digital identity. But this openness had a fatal flaw: it was built on trust.

By 1999, that trust was being exploited by the first generation of spam bots.

The crisis revealed how vulnerable the internet had already become. A motivated teenager with a basic grasp of Python could write a simple script that could interact with websites directly. These programs didn't need to understand the nuances of the internet. They just needed to recognise that, when they encountered an HTML field labelled "email_address", they should inject a string of random characters, and when they saw...