how risky are themes & plugins from wplocker

a friend of mine installed a few themes from the site wplocker or such a couple of years ago. i wanted to know exactly how dangerous these files can be on the system? and how can i take steps against it after removing those very files?

PS - now i know there are themes and plugins of WPMU dev there as well (of course, i chose the subscription instead). please be completely honest about the risks.

thank you!