Ghostbusters is a multi-media franchise created by Harold Raymis and Dan Akroid. The Ghostbusters are four individuals who run a paranormal extermination, extraction, and containment business. Occasionally they save the world too. There are two main lines of continuity for Ghostbusters: the official continuity (Movie 1, Movie 2, The Video Game) and the animated continuity (Movie 1, The Real Ghostbusters, the events of Movie 2, the NOW comic, Extreme Ghostbusters). Media not part of these continuities will usually stay close to the two movies, but will occasionally diverge entirely.
The Black Widow was a serial killer operating in New York City during the 1920s. She accpeted a proposal from Ivo Shandor to guard his spirit node at the Sedgwick Hotel. In the present time she exists as a ghost in the spirit realm, and has taked the body of a giant spider. Egon and the Rookie are thrust into battle with her, and have to avoid her web attacks and hordes of spider-children. Eventually she is defeated and the node disabled.
During the events of the IDW crossover Infestation the vampire Britt's spirit was corrupted by the Undermind and split off into four different worlds. In the world of Ghostbusters she manifested as a spirit, bringing the Undermind's zombie infection with her. Here zombies were reletively benign so long as a spirit remained within the body. Without a spirit, however, the zombie quickly turned violent and virulent. Rather than attempting to further the infection, Britt actually assisted the Ghostbusters in stopping the zombie outbreak. After the Ghostbusters had managed to vanquish the recently released and infected spirit of Gozer the Destroyer Britt left, taking a piece of Gozer's spirit with her for the Undermind.