Persistent malware notification on shared Mac mini

I've recently logged into my Mac mini, which is usually used by my members of my household since it is a shared computer. A malaware notification is constantly popping up and interrupting regular use of my mac. I've already emptied out the 'LaunchDaemons' & 'Launch Agents' folders of all things listed '.pist'. However, this did not solve this issue and it persists. Any help? Should I just bring it in the apple store?? I've only had this for about 3-4 years and I expected it to last a little longer than that.

[Re-Titled by Moderator]