When MySQL servers go weird

The MySQL PASSWORD() function has started giving a different value on a client’s live server compared to local development servers.

This has resulted in end users not being able to log in when PASSWORD()` is used to compare the stored and entered passwords.

Why this has happened I have no idea. Any thoughts?

dev
mysql> SELECT PASSWORD('foobar');
+-------------------------------------------+
| PASSWORD('foobar')                        |
+-------------------------------------------+
| *9B500343BC52E2911172EB52AE5CF4847604C6E5 |
+-------------------------------------------+
1 row in set (0.00 sec)

live
mysql> select password('foobar');
+-------------------------------------------+
| password('foobar')                        |
+-------------------------------------------+
| *9061D7B8DA0D4523AD448B53D80C2B551EDF8CD1 |
+-------------------------------------------+
1 row in set (0.00 sec)