Q: My iMac automatically updated Safari

Hey Startrekman,

I would start your troubleshooting the issue by seeing if Safari opens in another user on your computer. If Safari still will not then I would recommend reinstalling your Mac OS X Yosemite. The articles below will walk you through troubleshooting and isolating the issue and what to do after you have done this. Let me know if this helps or need further assistance. 

Mac OS X: How to troubleshoot a software issue

http://support.apple.com/en-us/HT201516

Isolating issues in Mac OS X

http://support.apple.com/en-us/HT203161

Take care,

-Norm G.