Helpful Links Regarding Malware Protection
An excellent link to read is Tom Reed's Mac Malware Guide.
Also, visit The XLab FAQs and read Detecting and avoiding malware and spyware.
See these Apple articles:
If you require anti-virus protection I recommend using ClamXav.
On starting Safari, I get a blank page with the simple message 'Fatal Error ownz you!' Everything seems to be working after that.
In that past that has meant that the site you use for your home page has been hacked by somebody that replaced it's content with the message you see. Your screengrab doesn't show us what the URL of your home page is, so I can't tell you much more than that.
It's certainly not any currently known malware.