## Turing test

**Stefan Kopieczek**explores his story.

A test invented by the mathematician Alan Turing in 1950 is helping to stop spammers.

*Plus*talks to

**Sir Roger Penrose**about all this and more.

**Mike Yates**looks at the life and work of wartime code-breaker Alan Turing. Find out what types of numbers we

*can't*count and why there are limits on what can be achieved with Turing machines.