I just got a windows 8 PC to use in my family room for ...well... the family. :-)
Two adults and two kids under 12. All are familiar with computers on various levels.
For my personal PC's I've never relied on anything but Microsoft Security Essentials as a anti-virus and malware solution. I've never had an issue, but I realize that has more to do with my careful surfing habits than the software 'protecting' me.
Now that the kids will have internet access (which is somewhat restricted by my family safety settings) I'm concerned they might inadvertently run into trouble. We monitor them very closely and the PC is in a public area f the house.
My question is does the consensus believe that I DON'T need any additional software beyond windows defender? If otherwise, what would be the best software solution?