A centaur in Greek mythology, Nessus, in a fit of lust, attempted to kidnap Deianira, the wife of Heracles. Heracles was the strongest man in the world and one of the best fighters in Greek mythology and he easily killed Nessus with a poisoned arrow. As a final act of malice, Nessus told Deianira, as he lay dying, that his blood would ensure that Heracles would love her forever. She foolishly believed him and, when her trust began to wane, she spread the blood on a shirt and gave it to her husband who died slowly and painfully as the blood burned his skin severely.
Nessus is a comprehensive computer security scanning program. It consists of nessusd, the Nessus daemon, which does the scanning, and nessus, the client, which presents the results to the user. It begins by running nmap to see which ports are open on the target and then tries various exploits on the open ports.