Except it's not. According to the office of the UN High Commissioner for Refugees in Malta, which gave me a leaflet about what words to use when discussing this issue, it's wrong to use the term "illegal". The reason is that most of those who arrive in Malta claim asylum, and even though they are locked up while their claims are processed, that detention is "administrative and not criminal". Also frowned upon is the word "clandestine", which has a "strong negative connection, invoking a sense of criminality". Instead, it recommends the phrase "irregular migrants".
