Mercedes caught with their pants down. Not sure how they will get out of this one unscathed.
Basically testing in season is banned specifically with current car and drivers, the car must be at least 2 years old. This has caused a massive stink amongst the other 10 F1 teams [us included] as it breaks one of the most critical rules in F1 laid out by the FIA.

http://www.f1plus.com/en/news/item/3...ll-a-hot-issue

http://www.grandprix.com/ns/ns25529.html