I have a Spring-MVC webapp deployed on a Hostinger VPS server (OS: Ubuntu 18.04, Apache2 + Tomcat servers). For some reason, every now and then, clicking on random regions within the web pages of my webapp causes malicious advert pages to open. The whole code for the webapp was written by myself and I have avoided using any malicious components. The VPS server itself was a clean install so I don't think that could be the source of these ads. I have tried this from multiple devices with the same result.
One thing I should point out is that the website is not running using HTTPS as I am yet to purchase an SSL certificate.
Is there a way to figure out why these ads keep showing up? What could possibly be the reason for these ad popups and what could I do to prevent this?