Cyber Security Virus/Scam

Every time I try to install a plugin or a theme, a cyber security virus (which is basically a message telling me to download this security system to my computer in place of the download option). I’m forced to exit out of my browser to abort it. It has not done this for all plugins, but it has occurred with downloading any and all of the themes, and it sometimes re-directs me to the malicious site simply by browsing the themes.

Does anyone know where I can find the source to my problem?

Site: komicks.com

Thank you in advance. I’m sorry if I cannot explain my problem much better.