Something for your students to discuss...

Pity the people who live in Isis Close in Cambridge. As far as Paypal is concerned, anyone living there is a member of ISIS. Clearly, the company uses an algorithm that prevents people living in an Isis-named road, or possibly companies that have Isis in their name, from using Paypal to purchase anything. (See Live on Isis Close? Then don't count on using PayPal: Web payment system blacklists addresses named after the Egyptian God in case they are terror-related.)

Thus, despite the fact that Isis was the name of an Egyptian deity, and that Cambridge is on the River Isis, as far as a Paypal program is concerned, "Isis" is associated only with the Isis we usually read about.

This is a good example of a bad algorithm -- or an algorithm that works only too well, depending on how you look at it!

How does the algorithm work? What is going wrong, in computational thinking terms? How could the algorithm be improved?