Norton Antivirus - Hosts File

[GingerSunshine]

Hello: I have Norton AntiVirus and Webroot Spy Sweeper on my computer. Recently when Norton AntiVirus runs a full system scan, Spy Sweeper informs me that Norton is trying to make changes to my HOSTS file and asked whether I want such change blocked. I don't remember noticing that before, but maybe I just wasn't in the room and Spy Sweeper blocked the change. I understand you are not suppose to let things change your HOSTS file. Is that right? Why would Norton want to? Should I let it? And I may have let it once a few weeks ago - is that cause for concern? Also, should I have more than the one Anti-Spyware program on my machine. If yes, any recommendations?
Thanks for any help.