How long is the antivirus and security 2010 valid for?

I bought the 2010 Norton security and antivirus nearly a year ago and I am now getting pop ups telling me I need to buy the 2011 version. Are they only valid for a year at a time? I have only used the 2010 package on one pc... am I able to reuse my 2010 antivirus again on the same pc for another two years? Very confused...

Thanks!