The answer to this is Worm. All of the choices are viruses that you would wish to never have but the worm is responsible for sending spam email to people that you know. A lot of people have been victimized by this type of virus. This usually appears in a form of an email. It may even appear to be a harmless email from you.
The moment that people you know open the email, the virus will spread to their very own computers. If they do not know about the worm virus, you will be accused of spreading the virus to their computers. Spam mail should be deleted at all times to avoid occurrences like this.
Worms are stand-alone programs that are often used to send spam emails, or emails containing viruses. Trojans often contain worms which are then installed for the purpose of sending spam emails, but the worms are what actually send the emails.