All back on again....but i dont have an account with them, looked them up, n at times people get this message without being part of them ??? perhaps to make people join ?
All I use is 'Microsoft Security Essentials' because I have tried just about everything going and they all clog up your system eventually...
...Norton is the biggest culprit and I wouldn't let it anywhere near any of my kit! I used Zonealarm successfully for years, until that too bloated and got uninstalled.
A computer geek collegue of mine recommended MSE and I haven't looked back since; it's also FREE to download!
I personally use Avast (free version) for antivirus and on the extremely rare occasion something gets past I use Spybot Search and Destroy to eradicate it.
Never had any issues (I don't use the resident portions of spybot as it's a really bad idea to have more than one anti-malware program running at once).
I'd also add that Norton is (at least the versions I've used which included Symantec corporate edition) a pile of memory-leak inducing poo!
Another vote for Avast, but you may want to consider downloading the portable version of ClamWin (link) and letting that run over the system too.
I always keep it (among with a selection of other portable apps and tools) on a USB stick on my keyring. You never know when it comes in handy.