Th e widespread use of so-called handhelds has produced the option that PDAs have a real potential for mobile access of centrally administrated applications in organizations. Th ese devices can be bought by anyone at reasonable prices, for example, via mobile phone contracts. Th is, however, has led to new types of security risks. Of course the potential risks already outlined for WLANs in general are still the same, but others, completely new ones, have been added to the list. And others in turn have aggravated already identifi ed weak spots. Before discussing the whole spectrum of these risk potentials and the ways and means to control them, an introduction into the system environment of these devices is necessary.