It's not too serious an infection insomuch as the beer being ruined. I agree with Palmer on this one. Sanitize a large spoon & skim it all of as much as possible. Otherwise it might cause off flavors. It's usually caused by inadequate cleaning & sanitizing of everything that touches the wort or fermented beer. Sanitize things right before use helps a lot in this regard. Freshly sanitized & used is your best protection,IMO.
If the beer's at FG,rack out from under it onto priming solution in the bottling bucket & get it bottled up.