I had a similar problem with 2005 (subs paid till 2007).
After weeks of trying to stabilise, I ended up getting rid of Norton.
Not only was it letting things in, it also wouldn't get rid of them,,,, & I couldn't get any help at all directly from Symantec.
This is no good when you pay for a product,,,, I only expected it to work !
Sorry I can't help