It's legit. It actually updates the contacts storage application - the version number of that will change when you install this, not the People app (sounds bizarre, I know.)

 

Oddly I've found my battery life seems to be improving since the app update

 

That would make sense, if they are having an issue with a constant pop-up (and associated background process) running constantly.

 

That's what I figured, the battery was draining a lot overnight which I found weird so I recon it was this process running even when the phone was on standby.

Lastnight it didn't go down at all over night

 

Aha! I just posted about this in the Significant battery drain Post JB thread, coming to the same conclusion. Great news, this must be the culprit.

 

Has the software number changed or was it just one app that updated?

Edit - Found this: http://androidforums.com/htc-evo-4g-lte/670618-android-process-acore.html

Then this: http://www.htc.com/www/support/content.aspx?id=191316

 

Just the People app, but what was updated now appears in the downloaded apps list as Contacts Storage version 4.5.538722.