Look this (this guy has similiar case)
http://www.experts-exchange.com/Software/Server_Software/Email_Servers/Exchange/Q_23741341.html
Exchange 2003 AD problem, MAD.exe, after changing admin passwords
Asked by UrsX in Exchange Email Server
Tags: Microsoft, Exchange, 2003 SP2
Hi everyone,
ever since we changed admin passwords (domain users administrator and
exchange admin), we have "strange" behaviour of Exchange. To be precise, it
is since the system-restart after changing the passwords. The problem may
also just be related to something else which took effect after the restart,
but I don't think so.
This is what we've got: every 5 Minutes 2 unsuccessful user logons (Security
event 529) by the domain administrator, Advapi, process 2560. 2560 stands
for MAD.exe.
_______________________________________________________
That's what I am talking about
There is no viruses or similiar threats, we have Sophos antivirus installed
and updated.
Regards