Many operating systems, however, do not implement RFC 793 exactly and for this reason FIN scans do not work as expected against these devices. Some operating systems, like Microsoft Windows, send a RST packet in response to any out-of-sync (or malformed) TCP segments received by a listening socket (rather than dropping the packet via RFC 793), thus preventing an attacker from distinguishing between open and closed ports. FIN scans are limited by the range of platforms against which they work. Additionally, because open ports are inferred via no responses being generated, one cannot distinguish an open port from a filtered port without further analysis. For instance, FIN scanning a system protected by a stateful firewall may indicate all ports being open. For these reasons, FIN scanning results must always be interpreted as part of a larger scanning strategy.