From their FAQ-&#62;Security page: 
"For security reasons Ipredator do not use any American software neither for encryption nor for any other part (we anticipate that most users will in spite of that use an American OS), but there is noting stopping an advanced user from accessing Ipredator with a more secure operating system or use a specific VPN-client."
I don't think I've seen a call to use linux worded like this before..