Robot

Any browser program which follows hypertext links and accesses web pages but is not directly under human control...

see "spider"

Computer software that runs continuously and responds automatically to a user's activity. Note: Some robots are created for the benefit of the user, such as those that send information when a user requests it, those that perform automated searches, and those that monitor messages in a forum and delete messages that are repetitive or violate the forum's rules of netiquette. Other robots are created to harm the user (e.g., a computer virus) or spam the user (e.g., a program that, whenever a user posts a message to a forum, automatically sends a response to the user containing unrelated advertisements).