REGEDIT4

[HKEY_CLASSES_ROOT\telnet\shell\open\command]
@="rundll32 url.dll,TelnetProtocolHandler %l"

[HKEY_CURRENT_USER\SOFTWARE\Microsoft\Internet Explorer\Main\FeatureControl\FEATURE_DISABLE_TELNET_PROTOCOL]
"iexplore.exe"=dword:00000000