Recently there have been reports of sharp spikes in visits reported by Google Analytics, this is seen as spikes in the sessions/users/visits graph in your monthly analytics report. If you look at the "Visits and Pages/Visit by Source/Medium" section of your report you will probably see a listing for social-buttons.com/referral which attributes for a fair chunk of your visits.
This is spam referrer traffic, they have never actually visited your site at all, they have just found a loophole in the Google Analytics system, and have randomly selected your Google Analytics ID and fed it to Google to create visits which are then counted. The object being that you will wonder who has made all these visits, and go and visit their site. Sometimes the site will be legitimate and be attempting to sell their service, other times their site will contain a trojan or other harmful code - do not visit the site! Because these spam referrals are not actually visiting your site, there is no adverse affect on your Google ranking (high bounce rates, when they only visit your homepage and then leave again will hurt your rankings).
Hopefully Google will find a fix for this issue shortly, and be able to filter out this information rather than including it in your reports. Until then, just ignore those visits in your totals.