#include <IE.au3>

GUICreate("Test User-Agent String", 700, 500)
_IEErrorHandlerRegister()
$oIE = _IECreateEmbedded()
GUICtrlCreateObj($oIE, 10, 10, 680, 480)
_SetUserAgent('User-Agent: đat đep trai.')
_IENavigate($oIE, "http://www.useragentstring.com/")
Sleep(1000)
GUISetState()

While GUIGetMsg() <> -3
WEnd

Func _SetUserAgent($agent)
    $agentLen = StringLen($agent)
    Dim $tBuff = DllStructCreate("char[" & $agentLen & "]")
    DllStructSetData($tBuff, 1, $agent)
    $chk_UrlMkSetSessionOption = DllCall("urlmon.dll", "long", "UrlMkSetSessionOption", "dword", 0x10000001, "ptr", DllStructGetPtr($tBuff), "dword", $agentLen, "dword", 0)
EndFunc   ;==>_SetUserAgent