Stopping form abuser

[mrgrammar]

The form on one of my sites is being filled out over and over again by someone who is using random characters. The results are like this:

FirstName: Chris
LastName: Chris
Address: wKQJDelTlpRINr
City: glLslryiCgHKQteRUIw
State: myNERFCSD
ZipCode: EHTtGujHSbFbBMM

All the fields appear in the correct order, and the email address field (which the script verifies) is always a properly formatted, legitimate-looking email.

Why would someone do this, and what can I do in my form processing script to stop this kind of thing?

[jeepin81]

get that users IP and block it from your form/site.

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[bradgrafelman]

Then again, since there are a plethora of free proxies out there these days, IP blocking is pretty much useless.

Have you tried adding a CAPTCHA? Perhaps adding some more validation to some of the fields other than just the e-mail address?