I have some anecdotal experience here - my supervisor at College in Britain in the 1980s was a Hungarian mathematician who left Hungary in the late 1960s having

I have some anecdotal experience here - my supervisor at College in Britain in the 1980s was a Hungarian mathematician who left Hungary in the late 1960s having had difficulties with the authorities. He vowed never to return to Hungary and had fairly trenchant views on the regime! Incidentally, my supervision partner was also Hungarian and has now returned and is running a bank in Budapest.