I never had any viruses doing harm to our puter. The virus killer updates automatically, the firewall is sufficient to control basics (only a hardware FW would be better) and SpybotSD gets rid of eventual spyware. Afaik: when you upgrade a bios and you get disconnected (no electricity) your puter won't work anymore and you'll need to have someone write you a new bios. It won't do something like partially destroying files. Apart from that: backing up is always a good idea. It's not a question of whether your HDD will crash, but when.