It's definitely necessary to have the best antivirus software for Windows 7 OS editions. The security solutions built into Windows can stop many threats that the average user may stumble upon. But this is the era of highly advanced online threats and malware including ransomware (which could hold your files hostage unless you pay up) as well as viruses which may quietly nestle in your system without your knowledge. Just don't think you are too clever to get a virus. Cyber criminals too are clever, very clever. You always need a good antivirus protection to combat them and their viruses.