spmug 579 Q. Why do some Web sites make you copy and type in a bunch of
hard-to-read twisted letters and numbers when you try to sign up for an
account or log in? 
A. That distorted set of characters on screen is
called a "captcha," a name that is really a crunched acronym for
Completely Automated Public Turing Test to Tell Computers and Humans
Apart. ("Turing" refers to the 20th-century mathematician Alan Turing,
whom many consider the father of modern computer science.) As you might
be able to guess from the name, the captcha is there to make sure it is
a live person trying to sign in to the page and not an automated script
or spam bot knocking. It's much easier for the human to scan and copy
the correct letters than for a piece of roaming code. There is more
information on the topic at www.captcha.net.