Downloading the software on MAC

So I just started looking into using the Mothur software for school. The problem it won’t let me finish downloading the software it says:

“mothur” can’t be opened because it is from an unidentified developer.”

Does anyone know how to over come this hopefully minor obstacle.

Thanks Kyler

This is because of the Gatekeeper functions on Macs. Here’s a link from Apple about it, http://support.apple.com/en-us/HT202491.