No viruses but there are some malware threats.
Download AdWareMedic, Ghostery and AdBlockPlus to keep your computer in A1 condition. Ignore all the windoze experts who will tell you there are Mac OS X viruses. Askthem to show you! In particular avoid Windows type AV as you have mentioned in your thread. Resource hogs that will slow your Mac. Even Apple sell this stuff, why? The old latin proverb I am afraid. A buck is a buck is a buck!
Download nothing from CNET o0r softonic which both include adware with their software downloads. Avast also does this.
Do not run any of the Mackeeper, CleanMyMac, TuneMyMac apps. Onyx which is free is recommended. Just download the correct version for you operating sytem which you have not shared, so cannot get you a link.