Sending Spam with Contact Form

If I get a note from my website saying that my feeback form did all this (below), what should I do? How do I secure my feedback form? Seems like people like to hack websites and screw you over. I’ve seen people make the user add two numbers to prevent getting spammed. But isn’t that kind of lame - forcing your users to do menial tasks.


it has come to our notice that a script you placed on your 1&1 web space
(contract id: 9047769) is being abused for the delivery of spam
mails.

The following script has therefore been disabled to prevent further abuse
of our infrastructure:

/index.php

Please also allow us to refer you to our T&C:

http://order.1and1.com/xml/order/Gtc section 7.14

Thank you for your understanding. Please secure your scripts against
unauthorized usage from third parties.

Regards,

--
1&1 Internet Inc.
Abuse Department