A while ago, the FBI introduced Carnivore, a net wiretapping system for
catching those crooks too stupid or ignorant to encrypt incriminating mail.
Now they've augmented their capabilities with a new system,
Magic Lantern. This is an email-borne worm
program which installs itself on the target's computer and logs their keystrokes, capturing passphrases and the like, and should work with on anyone
sufficiently stupid or ignorant to use Windows.
(Btw, anybody remember the old days when "email viruses" were a hoax which
circulated to gull clueless newbies, and everybody knew that you couldn't
get a virus from an email?)