Be careful here. A friend of mine was once caught and they were very specific. They let her go, because she had a valid air travel ticket out of Italy that particular day. The rules are not clear and vary from country to country, even though they are all supposed to have one border control policy. Don't take a chance, because even if chances of getting caught are one in ten - the chance of having to spend a night or more in a Italian or German prison is also 1 in 10.