It is obviously meant to make you nervous and think your computer will be exposed.
Symantec is a very good anti-virus application but it does cost money you don't need to spend.
My computer came with a free version (30 days) and I deleted it immediately. Somehow, it remembered it had been installed initially and sent me this reminder ... even though I never used it and 'completely' erased every instance I could find.
I am very hawkish on having excellent anti-virus updated regularly.
However, I do get upset when the anti-virus pay-for-service companies try to mislead non-techy PC users by these types of ads.
In my opinion - in the case of anti-virus and anti-spyware - the best is FREE.
Check out the free anti-virus and anti-spyware offerings I have been advertising (and use) on my Tools website.
If you have any questions, you know where I am.