My mom is having this problem happen on her computer. It also pops up when accessing yahoo home page from time to time. I install ad-aware, but maybe I will try removing that and using ublock origins instead. Or can both be used at same time? I will have to apologize to her, as I kept thinking she was clicking on a link that led to the site hosting this scam. Now it looks like it is a weird yahoo thing.
I installed AdBlock Plus in Chrome about five days ago and haven't had another problem - yet.
I don't know if this would help but I would think it's worth a try. Hopefully I won't have the
problem come back but before I installed AdBlock I would get the Security Alert code problem just about
every day and, as I said, I haven't had any problems for five days - fingers crossed.