Your caution and concern are admirable.
We should all be careful about where we browse on the internet, and what types of business we engage.
Many people I know in my local neighborhood are so cautious about the internet that they do not do any business, banking, purchasing or similar via the Internet.
That's fine. I personally like to make a limited amount of purchases at some sites, but many folks just decide to not do that.
They can still enjoy reading the news, checking the weather forecast, exchanging messages with loved ones, and participating in activities that interest them.
Through your hard work with Ken454, you have discovered that your own computer is not infected.
Through your hard work here at WTT Forums, with several helpers assisting, you have discovered that your experiences with yahoo are ordinary and the same as what other computer users experience.
If you continue to have high levels of concern about phishing and forged sites, I would encourage you to avoid submitting any personally identifying information, particularly avoiding information that may be related to banking and business.
If you already have engaged in business through the internet, consider going to your bank and credit card companies to change your username and passwords with them directly.
Then enjoy the Internet.
Do the types of things you enjoy, and benefit from the rich variety of ideas, images, stories, news, and information that is available via the internet.