Assignment of Thread IDs?
Failed Connection Attempts will still increment the Process ID next to be assigned

Here is an example:

I will restart mysql on my PC (MySQL 5.5.12) and connect for the first time

Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 1
Server version: 5.5.12-log MySQL Community Server (GPL)

Type 'help;' or '\h' for help. Type '\c' to clear the buffer.

mysql&gt;


Then I connect to mysql with an intentional bad password

I then connect to mysql with the right password

Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 3
Server version: 5.5.12-log MySQL Community Server (GPL)

Type 'help;' or '\h' for help. Type '\c' to clear the buffer.

mysql&gt;


and BINGO a MySQL Connection ID of 3 instead of 2

There is a record of it in the Global Status variables

mysql&gt; show global status like 'abort%';
+------------------+-------+
| Variable_name    | Value |
+------------------+-------+
| Aborted_clients  | 0     |
| Aborted_connects | 1     |
+------------------+-------+
2 rows in set (0.00 sec)

mysql&gt;


You evidently have connections still coming in from somewhere who can no longer authenticate. Maybe you could try using netstat and watch port 3306. If your have removed certain user@host values from mysql.user, then there is no need for real concern in terms of the process ID established and used.

You may want to run this query now and then...

SELECT hostaddr,COUNT(1) connections FROM
(SELECT LEFT(host,LOCATE(':',host) - 1) hostaddr
FROM information_schema.processlist
WHERE LOCATE(':',host) &gt; 0) A
GROUP BY hostaddr;


This will tell you how many connections are coming in per IP address or DNS Name