Illegal immigrants move countries to send money back to their homeland, for their family. Some do it for quality of life, others for better education. It can also be because they are hoping to escape wars.
The journey is very dangerous, many people die. If the immigration does go through successfully, they can end up begging and homeless. The migrants usually hide on boats and attempt to make it across to a different country. Libya is the heart of illegal immigration. This is because the Sahara desert is so wide that it is easy to cross without being found. It is also because the country is full of people smugglers. They then hide in boats, rigs and cargos to make it across.
One third of Malta's army budget is spent on tracking down on illegal immigrants, which is necessary due to the high rates of illegal immigrants in Malta.
It is a problem is because migrants are taking the money back to their country, causing the money rate to crumble. It is also because they are taking our jobs.
The EU is working on a rotation for migrants, changing every two years. This gives them a chance to earn money for their families.