Built For Designers & Developers

Myself also faced this situation especially I will get spam mails from the online essay writing services so, to get relieved form your problem The best option is to enable recaptcha, it\’s already a feature of k2 and can easily be turned on.
Select the k2 component in the admin area, then on the right hand side there is the toolbar button for Parameters, click that and in the box that opens under the section for Comments there is the ability to turn recaptcha on and inputs for the public and private keys that are given when you sign up and register your domain on https://www.google.com/recaptcha

Hope this helps.

Luke.
http://www.develodesign.co.uk