For the last three days com.avast.MacAvast.MAD %CPU up to 500%+ slowing down my late 2013 iMac with specifications below for your reference.
avast! Free Antivirus Version: 8.0 (40795), Virus definitions version: 14062501
Late 2013 Apple iMac (27-inch Display 2560 x 1440), 3.4GHz Quad-core Intel Core i5, Turbo Boost up to 3.8GHz, 8GB 1600MHz DDR3 SDRAM - 2X4GB, 512GB Flash Storage, NVIDIA GeForce GTX 775M 2GB GDDR5, Magic Trackpad, Apple Wireless Keyboard and OS X 10.9.3 Mavericks
I have been using Avast Free on PC's for 15+ years and on my iMac for these last 6 months and this is the first issue I have found with the software, but unfortunately I will have to uninstall it and rely on Avira Free Antivirus until this issue is resolved as the iMac unproductive in its current state.