Amazing mosquitoes

I don't know what to make of this.  I'm getting bitten by mosquitoes almost everynight even if I burn mosquito coils with the highest concentration of active ingredients available.

This is what I did last night:  I closed the window to my bedroom, lit up one mosquito coil next to my bed, and closed the door.  Then I was minding my own business just outside the bedroom for a couple of hours.

When it was finally time to sleep, the coil wasn't completely burnt yet.  I let it keep on fuming, left the door closed, but opened the small window (may I remind you, I live on the 18F, and there's no puddle of water nearby) because this coil smells too strong for me.  I went to sleep in peace, but then by 5:00 I woke up with at least four mosquito bites!  The only explanation is these bastards came throught the window!  This is astonishing.

Okay, so what I'll do tonight is the samething, except I won't open the window when I go to sleep.  But I thought these things are supposed to be used in well ventilated areas.  I hope this coil really kills the mosquitoes and only mosquitoes!