Recently, Yahoo sent out email telling users that their sign-in will be changing in October 20 and will be more secure. With that, they have notified users that old sign-in method after October 20 will no longer work. See below.
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We love that you love using your Yahoo Mail. And we want to make sure 
you always have the best experience. That’s why we’re reaching out 
today. 
                                    
                                    We’ve noticed that you’re using 
non-Yahoo applications (such as third-party email, calendar, or contact 
applications) that may use a less secure sign-in method. To protect you 
and your data, Yahoo will no longer support the current sign-in 
functionality in your application starting on October 20, 2020. This 
means that you will need to take one of the steps below to continue 
using Yahoo Mail without interruption.
                                    
                                    But don’t worry, you have options. Find an option that works best for you below:
                                    
                                    Option 1: We recommend that you access your email using our free 
Yahoo Mail app for iOS and Android or simply go to 
mail.yahoo.com to access Yahoo Mail on the web. 
                                    
                                    
                                    Option 2: Keep your current, 
non-Yahoo app, BUT follow a few steps to get it to sync with our secure 
sign-in method.  The steps vary across different email applications, but
 in most cases, you will have to remove your Yahoo account from the app 
and then add it back again to update the sign-in security.  Use the 
links below to follow the specific steps for your current application:
                                    
                                    
                                    
                                    
                                    Option 3: You can generate a 
one-time, unique password that will allow you to sign in to your account
 using your non-Yahoo email application.  Once created, this password 
will continue to allow your app to securely sync your Yahoo email unless
 you sign out (or are signed out) from your app.  You can find 
instructions on how to do this 
here. 
                                    
                                    If you want more details on these changes, please visit our 
help page.
 If you’ve already taken action, we’d like to think you haven’t read 
this far, but if you have . . . we sure appreciate the diligence!
                                    
                                    Thanks for rocking that Yahoo Mail address!
                                    
                                    Yours in your inbox,
                                    The Yahoo Team  
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Fine and dandy until you try to set up email using the Amazon email app on a Kindle. The procedures will not work and finally Yahoo in its HELP revealed that Kindle Amazon native email support will be discontinued. The only choice on Kindle is to get Yahoo email app from the store OR go to website for Yahoo and into mail that way.  So much for consolidating all email addresses into one app!
Well, this isn't the problem that now occurred. I did successfully on Thunderbird under Windows  delete my old account and add the Yahoo email back. But, somehow, TWO Yahoo email accounts then existed next time I brought up Thunderbird You would think a simple removal of one would fix the problem. WRONG. Instead, you now get an error that a "User Account by that Name Already Exists  ..." and this error does not allow removal or editing of ANY email addressed via the Tools-> Account Settings. Instead, I went to home page for Thunderbird and right-clicked one of the Yahoo Accounts. Then on resulting page I went to Account Actions and did remove. Did the same for other Yahoo email. Now added it back to establish new sign-in interface sync. That not only cleaned up the error for Yahoo, but did so for all other email accounts without having to do anything else. Go figure. NOW, I hope all is well!                                                              
While I find your idea of the software being hard coded to cheat based on the system clock really good, I don't trust either the FBI or the NSA to do that investigation. The FBI has been running a coup against Trump for four years and suddenly they're going to be honest?
The problem with doing forensic software analysis is that there's a hard deadline coming to certify the election and it's going to take time to do this through legal channels. And what happens if the Supreme Court finally hears the arguments in two years and the verdict is that the election was corrupt and stolen? Can they scrap it and order a do-over, or award the presidency to Trump after two years of Joe, the Ho, the squad and George Soros? Suspend all elections until every precinct in America works like, well, Florida and has its final results within an hour of the polls closing?