Web forms are now a routine target of spammers. Whether your web site is a personal one just looking for feedback or a commercial site generating sales leads, getting dozens of entries for link exchanges or online gambling sites isn’t anyone’s idea of useful feedback
It can be really disturbing when you started to getting lots of useless SPAM through the web form on your site.
Is there something we can do about it?
Luckily, the answer is yes.
I found few interesting articles.
Checking for the value of HTTP_USER_AGENT, if it is empty that means it is not from any browser.
Simple, but powerful. Having an extra text box but make it invisible using CSS, check if the textbox has any value in your server script. If the text box has a value in it, that means it is not a regular user’s input.
The demo page is here