Assuming you run antivirus software and have a firewall turned on, you can generally avoid malware by keeping all your software up to date and by not doing anything silly. Apple Macs and Microsoft Windows PCs are both vulnerable to malware. However, only Window ships with protection built-in. The awesome Microsoft’s Windows Defender.
1. No single antivirus program will find everything. Try at least two or more. It is a bad idea to install more than one antivirus program, but you can run one-off scans with as many as you like. Avast is a good option. ESET has a good free online scanner. Kaspersky’s Virus Removal Tool is another good option. Malwarebytes Anti-Malware and Spybot Free Edition(formerly Spybot Search & Destroy) can spot things other programs have missed. Malwarebytes’ (formerly Xplode’s) AdwCleaner targets potentially unwanted programs that some antivirus products leave alone.
2. No single scan will always find everything. Checking every file for every known virus could take hours, and some malware can hide other malware. If an antivirus program finds some malware, restart your PC, run it again and it may find more.
And while it’s useful to run antivirus programs in standard mode, you must run some scans after restarting your PC in Safe Mode with Networking. Safe Mode loads a minimal set of programs and drivers, which makes malware somewhat easier to spot.