Here is the Wikipedia article about Crime in Belgium. It seems clear to me and to the writer(s) of this article that Belgium is overall a very safe country, with some very unsafe areas corresponding to poor immigrant districts in big cities like Brussels, Antwerp, Liege and Charleroi.
Wikipedia said:Usually, serious safety issues in Brussels are mostly limited to residential boroughs with a low income population, mainly composed of North African immigrants. These include notably Sint-Jans-Molenbeek, Schaarbeek, Anderlecht, and Vorst. Recently, violent muggings (in several cases resulting in death) and cases of women no longer being able to wear revealing clothes because of violence committed by radical Muslims against them, have also been reported in other parts of the city.
...
Minors of non European Union citizenship, representing 4.4% of the population, are responsible for 24% of cases presented before youth judges. The share Belgian youths of foreign descent in cases brought to youth judge is 44%.
...
Terrorism and Crime
Besides general safety issues in some boroughs, Brussels reportedly serves as a hub for terrorists, as reported by various sources such as interpol, and local newspapers as Het Nieuwsblad and Het Volk. In the same boroughs that pose safety problems (e.g. Sint-Jans-Molenbeek, Schaarbeek, ...) there is active recruitment by terrorist organizations such as al-Qaeda. As stated by Hind Fraihi of Het Nieuwsblad the recruitment is done in backyard mosques.
...
Sexual assault
Sexual assault, including a number of gang rapes often carried out by youths of foreign descent, also happens.
...