United States v. Kelley, 482 F.3d 1047 (9th Cir. 2007)

You can protect your computer from viruses without expensive software. Instead, follow these simple tips:

Stay up-to-date on all system updates.

Don't download any email attachments you weren't expecting.

Avoid freeware and peer-to-peer sharing sites.

Use alternative web browsers and email software.