Some probes appeared to use IP-based scanning, such as several captures of the Lupper worm. When studied inside a virtual machine environment, the worm scanned a sequential range of IP addresses to see which, if any, were running a web server. If a web server was present, the worm attacked using several exploits that attempted to execute code on the server. IP-based scanning entails a relatively high cost per system infected in terms of search time and network resources, assuming a low density of targets. Worms which use search engines to locate their targets have a much lower cost per target because the search engine does the work of finding potentially vulnerable hosts.
Note that IP scanning will not work for name-based virtual hosts, a technique for hosting many websites on a single IP address that was introduced in HTTP 1.1. Using this method, the request for a web page has to contain the appropriate hostname, such as 'www.example.com' that is being asked for. Since there is no way for an IP-based scanning program to determine this name, there is no way for it to successfully exploit a site using virtual hosting. Name-based virtual hosting is popular with shared web hosting providers as they don't have to provied each website with a unique IP address.