There are 2 places that you need to disable logging at.  This 1st picture will disable logging of all channel/private message logs:

   [img:35cnhsex]http&#58;//www&#46;luniz&#46;org/images/logging1&#46;jpg[/img:35cnhsex] 

Set "Automatically Log" to None.

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This second picture will disable logging of all URL's posted in channel/private messages:

   [img:35cnhsex]http&#58;//www&#46;luniz&#46;org/images/logging2&#46;jpg[/img:35cnhsex]

Uncheck URLs & Emails for "Enable catching for"

Everyone needs to make sure that they disable logging in their mIRC clients.  The less traceability there is, the better.