The 4 levels of protection are as follows:
- Extended Organization Validated SSL Certificate:
An Extended Organization Validated (EV) Certificate requires validation of the company, the owner and the physical address of the company. An EV certificate will in most browsers show a green address bar and the company's name in the address bar. This makes it a lot more visible which company controls the website, and makes it harder for someone else to pretend to be the company online. It will also be part of showing the website as more serious than the competitors.
- Organization Validated SSL Certificate:
An Organization validated (OV) Certificate protects the data with full encryption and shows that the website and certificate belongs to the company that is registered in the certificate.
- Domain Validated SSL Certificate:
A Domain Validated (DV) Certificate protects the data by fully encrypting everything sent to and from the server. The certificate can be issued to someone who controls the domain, it doesn't say anything about which company is behind the domain, nor the certificate. If encryption of sensitive information is the primary objective and the identity of the company doesn't matter, then this certificate is adequate.
- No SSL Certificate:
An SSL Certificate is not always needed. If you have a static website where you don't receive information from customers, then an SSL Certificate isn't needed.