IEEE 802.11 works properly only if the stations respect the MAC protocol. We show in this paper that a greedy user can substantially increase his share of bandwidth, at the expense of the other users, by slightly modifying the driver of his network adapter. We explain how easily this can be performed, in particular with the new generation of adapters. We then present DOMINO (Detection Of greedy behavior in the MAC layer of IEEE 802.11 public NetwOrks), a piece of software to be installed in or near the Access Point. DOMINO can detect and identify greedy stations, without requiring any modification of the standard protocol. We illustrate these concepts by simulation results and by the description of a prototype that we have recently implemented.