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http://www.realvnc.com/products/free/3.3.7/winvnc.html#11

 [HKEY_LOCAL_MACHINE\SOFTWARE\ORL\WinVNC3]
 "AuthHosts"="-:+192.168:+193.77.104.3:"
 Type SZ

 This would deny all and allow everything from 192.168/16 and from 193.77.104.3/32