newclicks.com doesn't seem to exist on the web, unless you mean .biz. Either way, it seems to be a spam site, and I wouldn't be surprised if they're distributing malware. You or your son may have got a virus from them. Though the supposed attacks from your son's computer also could have been benign connections that were misinterpreted. It's hard to say exactly what's going on. But yeah, basically just check for malware now and then (checking daily is really overkill), and remember not to open strange attachments and stuff. And avoiding sites with lots of popups or using a popup blocker is also good protection from viruses.
But it sounds like Norton is doing it's job, so I wouldn't worry too much unless it continues. If it does, I would focus on your son's computer, as it seems to be the source.
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"If knowledge can create problems, it is not through ignorance that we can solve them." - Isaac Asimov