Your web host most likely runs a nightly and a weekly back up of your entire website. Do not make the mistake of assuming this provides all the back up support you need. Back ups can fail and your web host does not make any guarantee about them for this reason. Consider that it's handy to have quick access to hosting back ups but again – do not rely on them. Take your own steps to back and safeguard your website.
I use Backup Buddy from iThemes to run my own nightly backups and store them over on Amazon s3 hosting – away from my own server should there very be a major failure there.
Stepping Up Your Defenses
You can pay someone else to run your back ups and verify that everything is properly taken care of. Lynette Chandler offers Auto Site Saver.
Paul Taubman, the Digital Maestro, also provides back up and security monitoring services.