This is not a first occurence out of africa, and as for the walk-around, it is very easy to hide in a wheel well of a wide-body.
Next time, imagine where you'll hide and what is the chance of someone finding out after that. Rather remote! esspecially during night. Departure times out Dakar was??
You have to spot the guy BEFORE he climb inside the wheel well.
My previous airline put special security in place after a similar incident roughly 10 years ago, it is obviously a big security breach.