Show Users That Connect To DB
You can record every connection using the general log.

In fact, you can record that information into a table. 

In the mysql schema, there is a table called general_log. Here it is:

mysql&gt; show create table mysql.general_log\G
*************************** 1. row ***************************
       Table: general_log
Create Table: CREATE TABLE `general_log` (
  `event_time` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
  `user_host` mediumtext NOT NULL,
  `thread_id` bigint(21) unsigned NOT NULL,
  `server_id` int(10) unsigned NOT NULL,
  `command_type` varchar(64) NOT NULL,
  `argument` mediumtext NOT NULL
) ENGINE=CSV DEFAULT CHARSET=utf8 COMMENT='General log'
1 row in set (0.01 sec)

mysql&gt;


Of course, the table uses the CSV storage engine. You can change that to MyISAM and index it. Make a copy of the table beforehand:

use mysql
CREATE TABLE general_log_copy LIKE general_log;
ALTER TABLE general_log ENGINE=MyISAM;
ALTER TABLE general_log ADD INDEX (event_time);


To activate it, do this

1) Configure the general log to record to a table by adding these lines to my.cnf

[mysqld] 
general-log
log-output=TABLE 


2) Restart mysql

3) start mysql and user it for a day or two

4) Look for the dev user by running this query

SELECT * FROM mysql.general_log WHERE user_host LIKE 'dev %';


This will tell you what time and what IP dev is coming in

5) Hunt down the dev user in all your code

6) Truncate the general log

SET @old_log_state = @@global.general_log; 
SET GLOBAL general_log = 'OFF'; 
TRUNCATE TABLE mysql.general_log; 
SET GLOBAL general_log = @old_log_state; 


7) If you did find 'dev' users sneaking in, wait 24 hours and go back to step 4. Otherwise, you're done

CAVEAT

Please disable the general log when you are done by removing the lines in step 1. After that, just run

SET GLOBAL general_log = 'OFF'; 


That's all !!!

Please see my posts about the table version of the general log:


Jan 28, 2013 : mysql logging activity from specific user or ip
Feb 11, 2012 : MySQL general log
Nov 16, 2011 : Log MySQL DB changing queries and users


I also did this using the slow log instead : How to do MySQL User Accounting

Give it a Try !!!