My internet speed has slowed to a crawl after installing security update 2015-003. Any ideas on how to fix?

I have a mini mac with 8GB ram and running yosemite OS. I recently installed security update 2015-003 and now my internet connectivity have slowed to a crawl. sometimes if I turn wi-fi off and then back on the speed returns to normal but sometimes it does not. Any ideas what may be causing the slow internet speed?