Your Little Brother Came for a Visit and Used Your

Your little brother came for a visit and used your laptop. You didn't think anything of it at the time, but now your laptop is running really slow. Which of the following statements is false?

A) It can't be a worm because your anti-malware software would have blocked it.
B) It can't be a Trojan horse because your anti-spam software would have blocked it.
C) It can't be your brother's fault because he only visited Web sites, and he didn't open any files.
D) Your brother admits to opening a joke file on his e-mail, but the file was from a good friend, so it can't be your brother's fault.
E) All of the above statements are false.