If your Mac is operating at a slow pace, then for that reason alone it is worth the upgrade to OS X 10.6 Snow Leopard.
Free antivirus for os x 10.6.8 for mac#
Includes a 30 day trial of Sophos Home for Mac Premium, with advanced ransomware scanning in real time.
Mac OS X 10.6.8 Snow Leopard is an upgrade to the previous version of OS X Leopard.