This was posted in "Poll: Manual Scanning" by Floating Red that got my attention:
It is up to you if you want to do Full System Scans Daily or not; if it makes you feel better, then feel free to do it. We only can suggest things for the User to do. Also, if you are asleep, you are not using your computer, so it will not hurt. What I would strongly suggest would be to Disconnect from the Internet before going to bed so that, if Norton AntiVirus 2008 finds anything and Removes it, you do not get re-infected.
My questions are:
1. What is the purpose of disconnecting from the internet and is it good practice to disconnect from the internet during scans ?
2. During a Full scan in progress, is my computer still protected from infections ?
3. How does a computer get reinfected if Norton finds and removes a infection while connected to the internet ?
This is not the first time I've seen this posted in other posts by different people about disconnecting from the internet while doing a scan.