A self-signed SSL certificate is an identity certificate signed by its own creator; however, they are considered to be less trustworthy.
Self-signed certificates cannot be revoked, which may allow an attacker who has already gained access to spoof an identity if a private key has been compromised. CA signed certificates have the ability to revoke a compromised certificate, which prevents further use.
Because of the security risk, we recommend that you use the shared SSL that comes automatically with your shared or reseller account. Otherwise, we suggest that you purchase a secure SSL certificate, instead of using a self-signed certificate. On a VPS or dedicated server, you are welcome to install your own self-signed certificate, although we still do recommend that you install a CA signed certificate instead.