Norton Internet Security 2012
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Full user review
"Needless Fiddling with 2011 version"
None, over the 2011 version.
NIS 2012 is, in fact, slower for many people. Check the Norton AV/NIS thread at the Norton Users Forum at Symantec.
I myself tried upgrading to NIS 2012 and it was palpably slower in all respects compared to 2011. I'm staying with 2011 until Symantec offers an update to correct this.
Symantec tinkered with what could be NIS's best version ever, namely, 2011. There IS a slowdown, no matter what reviewers say. Not everyone is running quad-core. Symantec stumbled here, after three successively improved versions (2009-2011).