Nearly everything with a form can get spam by those nasty spammers. Somehow they have an automatic program that is able to automatically spam without them visiting your website at all! It's just like a daily routine for them to promote their site but for us, it's a daily annoying task to delete spams on our guestbook, blog, wiki, comment and etc...
One of the best way to counter this problem is by using CAPTCHA. A CAPTCHA is a program that can generate and grade tests that most humans can pass, but current computer programs can't pass. For example, humans can read distorted text as the one shown below, but current computer programs can't.
Many of you might be already using a contact form that works and it's just troublesome to update the whole code to support CAPTCHA. Moreover, your webhost must support GD library for verification of the image. I found a solution to this problem which you only need to update ONE line of your form to have the CAPTCHA feature.
Protect Web Form provides free CAPTCHA service. It only requires 3 steps to start using their FREE CAPTCHA service on your forms to prevent spambots. Good thing about Protect Web Form is that it also supports Audio. Meaning if you can't see the random letters and numbers, clicking on the small speaker icon will read the letter and numbers.
1. Create account on http://www.protectwebform.com/
To do this, just go to the registration page: signup and fill in all the fields. The new password will be sent to the email address which you provide.
2. Login to the http://www.protectwebform.com/
with the login name you provided and your new password. Go to the page My Verification Urls and click on the button "generate". You will see two urls, which will be used to show the image and to verify the code.
3. Click on the link 'Install', choose type of installation and follow a few short instructions on that page to install the protection scripts.
1. Update you html file as described on the installation page.
2. (If required) update you code file as described on the installation page.
CAPTCHAs do have drawbacks; the main drawback to any CAPTCHA implementation is that is makes it almost impossible for visually impaired individuals to use. In some cases, even those users who are not visually impaired may have a difficult time reading the CAPTCHA string since they are designed to be difficult to read. Also, there may be accessibility laws in your area that you must conform to as well.
CAPTCHAs are not fool proof and they are not a final solution against spam bots. OCR (Optical Character Recognition) has been used to break many CAPTCHA implementations. Also, there have been reports on using cheap 'sweat shop' labor to get around CAPTCHA implementations by having people perform the registrations en mass.
It is not perfect, but CAPTCHA provides an additional level of defense against spam bots.
[ Use CAPTCHA Service to Prevent SPAM ]