WUPS

The WUPS application was designed to be a small, easy to use Windows UDP port scanner.

How does the Delay affect the result of a scan?  The Delay is very important for a couple of reasons. First, each port you scan will cause over 85 bytes to be transfered over the network (the exact amount depends on the kind of network). Say that your connection can only handle 5kb per second. If you scan with a delay of 10 ms, that will generate over 8.5 kb per second, and the scan will choke.

This is nothing new, the same happens with TCP port scanners. The second thing is that this UDP port scanner relies on the fact that the scanned system sends back ICMP packets. A lot of machines limit the number of ICMP packets that may be sent in a specific time interval.

The limit depends on the kind of system, sometimes a Delay of 50 ms will do, sometimes 500 ms will do, and sometimes you have to scan with a Delay of over 1000 ms. If you reach the systems limit, it will choke and you have to wait a while and then restart the scan. If you scan a Windows machine you can usually set the Delay as low as the network connection allows, since Windows doesn't have any ICMP limit.