The defendants were convicted in 2009 of one count of conspiracy for selling day traders access to the information that came from the internal squawk boxes, allowing the traders to beat larger firms to orders on securities.

FORBES: 'Squawk Box' Defendants Denied Bid For New Trial

Walgreen may not know for certain which plans are steering big orders to mail vendors, but says it will find out using internal sleuthing.

FORBES: On The Cover/Top Stories