Which type of alien software uses your computer to send emails that look like they came from you to all the people in your address book?

Spamware

Explanation:

According to my experience in the field of information technology and cyber-security, i can say that this is called Spamware. This is a software designed to manipulate emails, one function is to be able to fake emails from a victim and forward that email to all of the victims in the clients address book. Other functions include generating random addresses, inserting fake headers into email messages, and even activating various mail servers at the same time.