We all know that contact forms on websites can attract a degree of spam comments but these can be minimised with a few simple measures.
In case you don't know, a lot of comment form spam is generated by automated form spam bots that travel round the web filling in forms with computer-generated names, email addresses and messages. They do this to get people to click on links or promote a site for SEO reasons (although this is usually ineffective).
Don't get me started on CAPTCHA methods. In my opinion, they are the wrong way to tackle this because they push the onus of prevention onto your regular users, making it more difficult for anyone to complete a form.
However, to stop automated form fillers that create spam, it's often enough to add a simple, validated question like "What is 3 + 5". This is easy to answer for any real person but automated spam bots will often fail on this (as long as you have the appropriate checks/validation in place). As a result, their form comments don't get submitted. Hurrah!
I also recommend Akismet for identifying and filtering out comment spam. It's very accurate because it uses a massive database comprising millions of blogs to to do this. Akismet is free for non-commercial sites and costs a few pounds per month for others.