A port scanner is a piece of software esigned to search a network host for open ports. This is often used by administrators to check the security of their networks and by crackers to compromise it. To portscan a host is to scan for listening ports on a single target host. To portsweep is to scan multiple hosts for a specific listening port. The latter is typically used in searching for a specific service, for example, an SQL based computer worm may port sweep looking for hosts listening on TCP/UDP port 1433.