Bitdefender
This amazing free protection against existing and new e-threats is quick to install. Being light on resources, it is the only antivirus you need on your Windows computer.
Finds Mac malware as well as Windows viruses for free. You can scan running apps, critical locations, a specific location or your entire system. Don’t pass malware along unknowingly.
Kaspersky
Free lightweight Virus Removal and Anti-Ransomware tools to clean up viruses, trojans, malware and adware AND scan and block ransomware and crypto-malware.
Sophos
This powerful tool detects all types of malicious software on your Windows computer (including viruses, spyware, rootkits and Conficker), and returns it to a working state.
Trend Micro
A free online scanner for Mac and Window that lets you quickly find new threats without getting in the way of the existing security software on your computer.