Final answer:
Intruders use virus signatures to fabricate the origin of an e-mail.
Step-by-step explanation:
Intruders use virus signatures to fabricate where an e-mail came from. A virus signature is a unique pattern or code that identifies a specific virus. By using virus signatures, intruders can manipulate the information in an e-mail's headers or content to make it appear as if it originated from a different source.