Hi I was surfing the web when my web address was suddenly hijacked and Microsoft security warning with a warning label "S3.amazonaws" appeared and my screen just froze still. I has to reboot and do a systems restore before it was fixed. 

My question is, why is there a bug when my system had already been installed with the latest updated Microsoft security essentials antivirus software? 

Is there any way I can prevent another hijacking of this sort?

Pray explain and any advice is appreciated from the community out there.

Thanks

James