404 on a file in our website

I loaded WPMU floating social plugin only to find out it can't be used with Upfront. I deactivated the plugin.
I recently learned I've had a few hits on a file that I'm not familar with, but it leads to a 404 Page. Here's the link: http://www.marketingcommunicationsgroup.net/sharebutton.to
Today I had almost 100 opens on this in my Google Analytics.
What is it and what should I do?