Your copy of EM is probably polling the server; turn off polling on the system through EM.

Another thing to note (we got bit on this one):  do not "hide" your MSSQL 2K instances.  This is documented in the KB.

One last thing - we found that when running multi-instance installations of MSSQL, even thought 1434 is blocked at the border, I can connect to and work with non-default instances of MSSQL from beyond our borders.  This means that MSSQL is using ports other than 1434 for authentication when running a multi-instance system.  This is not documented, and a port scan would probably reveal the ports in question.  Just an interesting thing I noticed.