A friend of mine had a couple of old websites break after their host upgraded to PHP 5, and I imagine they also upgraded the MySQL databases as well at the same time.
This was the error:
Connection error: Connection using old (pre-4.1.1) authentication protocol refused (client option ‘secure_auth’ enabled)
Unfortunately, the host didn’t allow mysql.user configuration changes, so it took me awhile to figure out a workaround.
What I finally discovered, hours later, was that simply creating a new username/password was sufficient. Basically 1) create a new user attached to the MySQL database, 2) update any software config files (in this case for Moveable Type and Media Wiki) with the new database user credentials. And then everything worked again.
I thought I would put this here in case anyone else ever needs it.