Good references Puntuado con 4 de 5 estrellas
On Webutation's 'about' page is mentioned :
* Google Safebrowsing against badware an phising fraud (which is used in Firefox as well and updates every half hour).
* Website Antivirus which scans sites against adware, spyware and viruses.
* WOT which collects some reviews about websites.
I believe the idea is to aggregate different sources and sum up a global score. The idea is good, let it grow.