A method of identifying wireless transmissions carried on a wireless local area network, 'WLAN' for analysis, the method comprising a wireless network sniffer device: receiving, at an interface unit of the wireless network sniffer device, over a dedicated link from a network management system controlling the WLAN, network identity signature data associated with the WLAN; detecting, at a wireless receiver of the wireless network sniffer device, wireless transmissions; identifying network identity signature data from each wireless transmission; comparing the network identity signature data received at the interface unit with the network identity signature data identified from the wireless transmissions to identify which of the wireless transmissions were carried on the WLAN; dropping any of the wireless transmissions not identified as having been carried on the WLAN; and capturing any of the wireless transmissions identified as having been carried on the WLAN for analysis; the method being characterised in that comparing the network identity signature data received at the interface unit with the network identity signature data identified from the wireless transmissions to identify which of the wireless transmissions were carried on the WLAN comprises: classifying a Basic Service Set Identity, 'BSSID', in the network identity signature data identified from the wireless transmissions as belonging to the WLAN by determining that it closely matches a MAC address in the network identity signature data received at the interface unit; and classifying a Service Set Identity, 'SSID', in the network identity signature data identified from the wireless transmissions as belonging to the WLAN by determining that it closely matches an SSID in the network identity signature data received at the interface unit, where close matching is determined when octets are compared and found to differ by less than a defined number of bits. receiving, at an interface unit of the wireless network sniffer device, over a dedicated link from a network management system controlling the WLAN, network identity signature data associated with the WLAN; detecting, at a wireless receiver of the wireless network sniffer device, wireless transmissions; identifying network identity signature data from each wireless transmission; comparing the network identity signature data received at the interface unit with the network identity signature data identified from the wireless transmissions to identify which of the wireless transmissions were carried on the WLAN; dropping any of the wireless transmissions not identified as having been carried on the WLAN; and capturing any of the wireless transmissions identified as having been carried on the WLAN for analysis; classifying a Basic Service Set Identity, 'BSSID', in the network identity signature data identified from the wireless transmissions as belonging to the WLAN by determining that it closely matches a MAC address in the network identity signature data received at the interface unit; and classifying a Service Set Identity, 'SSID', in the network identity signature data identified from the wireless transmissions as belonging to the WLAN by determining that it closely matches an SSID in the network identity signature data received at the interface unit, where close matching is determined when octets are compared and found to differ by less than a defined number of bits.