There seems to be a new kind of security software available - most recently, Norton 360 appears to be creating competition for Windows Live OneCare.

I didn't quite figure out what the main differences are, though. Any help?

As far as I can tell, Norton will offer more features than onecare. Norton is big on online transaction security, and Norton 360 is no exception there. So you will have software to check for malicious or fraudulent websites, it will check if you are using your passwords only on sites that are cleared, etc.