"The particular case here relates to suspected fraudulent credit card use for purchases made in the Live Search cashback program. We've filed this John Doe complaint as a step in the discovery process to enable us to get additional information from third parties for our investigation."
In other words, Microsoft admits that they don't know if there was any fraudulent activity. They admit that the only reason they are filing this lawsuit is that they hope it will reveal information which may indicate fraudulent activity. In other words, the very definition of a fishing expedition.
Remember back in the day when you actually had to have proof BEFORE filing a lawsuit?