Verification codes?

Hi all! regarding those little alphanumeric verification codes you have to type before submitting payments, emails etc- what are they called and where can I find software to install that on my boss's website? We are getting mauled by spambots (mostly for Viagra and German hookers... does anyone need that much Viagra? Maybe cuz of the German hookers, I guess. ) which are causing me to miss legitimate registrations for our workshops. I have searched endlessly and can't come upon the proper search term to find what I am looking for.... thanks! kat

 

A couple to look at :

http://captchas.net/

http://recaptcha.net/whyrecaptcha.html?gclid=CIylvKqd5I0CFR8SQQod8k1trQ

Btw, moving thread to Software Forum

 

Lev! Thanks again! (and sorry about the German hookers comment, but MAN, we get at least 20 when I open the email in the morning, so that wasn't a totally salacious comment) I wasn't sure where to post that, tks for the BTW.
Best of the weekend to you, kat