You were replying to e-mail when suddenly your computer started to display random messages, and stopped responding to keyboard and mouse input. You suspect that you have accidentally downloaded a virus. Which of the following actions most likely caused this?
A. You opened an e-mail attachment.
B. You sent an e-mail message with an attachment to a co-worker.
C. You logged in to your company's portal.
D. You printed a file that was stored on your hard drive.