Hi there,
just to follow up on this for people who might have the same question in the future:
Almost every time I log on from another location than home (well okay, basically when in another country) my account gets locked temporarily. Be it the UK or Mexico, they lock it until I call them and tell them it is okay, it really is me.
When I tried to log on in the US they locked it too and wouldn't unlock until I was home again - when I got home and called them they unlocked it without any problems.
As a funny side note: I contacted them via email first while in the US and called later since I received no immediate response. A few days later I received an email stating my account had been locked because I already possessed another account. Well, of course I do, d'Uh - at one point of time I wanted to change the currency on my account and they advised me to open another account with another email address in the new currency while they would lock my old one and transfer my funds.
Funny how they don't seem to know their own SOPs..