It appears to pop up only on my computer and only on CCF.
Interesting. Considering that it's only happening to you, and only on one computer, the most likely issue is that you have malware on your computer. Do you have an anti-malware program? I recommend Malawarebytes free version, myself.
If that doesn't solve your issue, I will pass it along to proboards, but I'm 80% sure that's going to solve it.
Also, are you actually still using Flash on your browser? If not, try uninstalling any version of it you still may have on your machine. Most browsers and websites stopped using it a few years ago because of its security flaws.
Just want to make sure you saw proboards' response:
It may have been an ad. If it was an ad, it should have already been detected and be in the process of being removed, if it hasn't been removed already. I know he has run malwarebytes, but it may be prudent, if he hasn't already, to clear and cookies in the browser. If he continues to have a problem, please post back."
I mean erased everything on my computer and start over again.
Yikes, George! No one asked you to do that.
If you're sure you wiped EVERYTHING, including the cookies, why don't you speak to proboards directly so that you can get to the bottom of this more efficiently without me as a middle man? Who knows -- maybe it's in your wireless router or something.
Here again is the discussion I started with proboards help. Why not chime in yourself and speak to them directly?