Petzl is warning that they have found counterfeit versions of several of their products. They are not manufactured to the safety standards that are printed on the products, and so are very dangerous for use as climbing equipment.
In the post on their web site they have identified four products are being counterfeited: the Croll ascender (B16), the Attache carabiner (M35 SL), the Ascension ascender (B17), and the Rescue pulley (P50).
Some of the equipment breaks at 2/3 of the specified strength. The items do not meet UIAA or CE standards.
Particularly troubling is the pulley, which is a rescue pulley used for industrial rope access, and rope rescue all over the world.
Petzl does not give any advice on how to identify the counterfeits, claiming that it is very difficult, and mentions that only a few have been found and none in North America. Their advice is to only purchase from authorized Petzl retailers.