What is the best way to build a contact form using PHP that stops hackers and spammers most effectively?

I was wondering if you can give me some suggestions or point me to some tutorials inorder to accompli开发者_StackOverflowsh this?

I use googles recaptcha. Works great.

For blocking spammers, you should use Google's reCaptcha like @Byron said.

For some advanced security issues, I'd recommend taking a look on the OWASP site. The OWASP project defines a list called the Ten Top Project where the most common security issues on web applications are stated and how to solve them.

Also, for some more security articles on security using PHP I'd recommend Chris Shiflett's web.

Perhaps Im giving you too much material for a single contact form, but the security level is determined only by you, I can only point some good resources. Hope you find this helpful