Either you are looking for a free internet security software or a one-time payment lifetime license deal. I believe there is an option for you.
One option that comes to mind is AVG’s Antivirus Free. According to their website, under “Free Antivirus”, you’ll see their tagline “Installs in moments. Protects your PC forever.” Those are bold words to declare for your free antivirus. AVG Antivirus Free provides BASIC protection. For your internet security needs, it stops viruses, spyware, ransomware, and other malware and blocks unsafe links, downloads, & email attachments. It provides all-around protection and gets real-time security updates.
There are those who offer “lifetime licenses” online. Some say that they provide a lifetime license [with a serial key] but it is most likely a 1-year or 2-year license for the software. For me, it sounds nice to have a lifetime license for software that you use daily. It is true for software like maybe Adobe Acrobat Pro but for software that continually renews and grows along with emerging threats, I’d rather have an annual renewal of it. Renewal of subscription is a small price to pay for those who tirelessly keep our webspace secure.