Neilsen's 5th symphony was an early example (1922). Towards the end of the first movement, the side drum part is in a different tempo and time signature from the rest of the orchestra. The first edition of the score instructed the drummer to "improvise as if at all costs he wants to stop the progress of the orchestra". 

In a later edition that instruction was replaced by a written part which breaks off with the direction "cadenza ad lib".

Skip to about 14:45 here: 
            
                
                    
                    
                    
                    
                    
                
             (There is also an important side drum part in a more "conventional" rhythm earlier in the piece.

What is it called when a music has two concurrent tempos
A well known CMS called Joomla allows users to register and the password appears hidden as you register with dots a normal experience online - at this point you think just you know it. But if the site is using http then in fact the password is POSTed using plaintext.

This shouldn't be allowed!

I can understand that passwords are stored as salted hashes in good systems so even if the passwords are discovered on the db you cant use them to login.

Is that pretty much it? 

Before we talk about password reset - in this case a good system cannot remind you of your password as it is not recoverable! It can only reset it for you and again isn't this sent plaintext over the net ??? So why cant that get stolen..

The issue is when the real plain text passwords are known by anyone or any system other than the user then identity is lost. 
