A fictitious piece of information added to a work of reference in order to catch information thieves and plagiarizers. The publisher of the work can use the offender's own product as evidence of copyright violation in court.

For example, a map publisher might add a phony road or a spurious label to one of its products. If someone publishes a photocopy or tracing of the map, or worse, digitizes it into a GIS database, the nonexistent object will appear in the stolen product.

One can imagine a mostly-innocuous software bug being used as a copyright trap.

Perhaps this explains Microsoft. Nahhh....