Unfortunatly, the website is down due to an error in traffic calculation.
We usually use 30-40Gbytes per day and we have 1200Gbytes of traffic per month, so enough for each month.
But the 14 and 15 April, their system say we use 688 and 884Gb (= more than 10Mbytes/sec for 24 hours) of traffic (so 20-30 times what we usually use) thus exceeding the allowed traffic per month.
I'm contacting them to try to fix it as soon as possible.
Here is an update: http://aircrack-ng.blogspot.com/2009/04/paying-bill.html