I did not know about this - it was enough to finally make me change my PP password (Ebay password as well).
Apparently scammers can swoop in to your PP account, print Express Mail postage to Russia and other countries to the tune of hundreds of dollars. The good news is that PP will usually not hold you accountable for the charges. So if you get a notice in your email that you printed a shipping label, and you don't remember doing it, check it out. You can read about it here. It has happened to a bunch of people.