That you have to take the phone to the service counter and ask them to "flash my phone."
Here's where I noted it. https://www.cnet.com/forums/discussions/malicious-advertising-turn-off-allow-third-party-apps-now/
More questions. Did you leave the third party apps on? If so, read that link.
Is this just a browser redirection? Factory reset would clear that.
Purple dots sounds more like a failing hardware issue. Why do you think it's a virus?
I got a virus on my cellphone. I did a factory reset but the hundreds of purple flickering spots still cover my entire screen. I've tried every mobile virus scanner. I have an LG Optimus zone 3 vs425pp8.

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