With a botnet of 25,000 computers, you could break the security codes for Amazon.com, you could raid people’s accounts, you could get social security numbers and data — there’s almost no commercial security system in place that couldn’t be breached by a supercomputer of tens of thousands.

— As many as 12 million computers worldwide have been infected with a highly-encrypted computer worm called Conficker. Writer Mark Bowden details how Conficker was discovered, how it works, and the ongoing programming battle to bring down Conficker on today’s Fresh Air.