You should ensure that the antivirus application is up-to-date with regards to the version and the virus definitions: since people are creating new viruses all the time, the antivirus application must be kept up-to-date as far as knowning what is new to protect you. Does it come with a scheduled updater so you don't have to remember to do the updates? IMO, the antivirus should have two things: a real-time protector which runs all the time the computer is on and is continually scanning what is happening in real-time. This will protect you when you are on the internet or you accidently open a virus infected file. You will often get a message (pop-up)telling you that the anvtivirus has discovered something unsavoury and what it has done with it. The second thing is an e-mail application protector. This is more important if you use office applications to look after your e-mail like Outlook. Since the majority of viruses are spread through e-mail you want whatever is looking after your e-mail to be covered. To answer your first question, I would scan the entire computer hard drive or do a full system scan as viruses can dump themselves in many places. You can never be too carefull even with Macs.