I know there are many questions going on this very topic - like why the Triwizard Cup Portkey was two-way and why the Portkey didn't return Harry and Cedric to the center of the maze, where it was originally placed. But my question is a little different...
In book 5 when Dumbledore created a Portkey and sent Harry to his office from the Ministry, Fudge told him that creating a Portkey like this is illegal ... and since all illegal activities are closely monitored by the Ministry, be it underage magic or Unforgivable Curses, this activity must also be closely monitored.
Secondly, in book 7 I supppose, it was told to Harry that the Floo Network and Apparition are closely monitored by the Ministry and it is worth their lives to create an illegal Portkey, so that was why they used brooms to fly him out of his home.
Now coming to my question -
How come Barty Jr. created a Portkey, a powerful one to carry someone hundreds of miles away from Hogwarts grounds, and still this activity was not noticed and brought to the attention of Dumbledore or the Ministry?