The University is located in the seventh arrondissement, which is the heart of Paris, and it's surrounded by many historic landmarks which are almost always populated by tourists. It is a very secure area, and it is uncommon to walk more than a few blocks without finding a police car on patrol. The University itself is considered a secure place by its students, who don't think twice about wandering in the surrounding area into the early hours of the morning on the weekends.
It is easy to forget that Paris is a big city when the University and its students are situated in such a safe location. However, it is important to keep in mind that there are places in Paris where it is not the best idea to venture out to on one's own or late at night. These areas are usually unappealing to students anyway, since they do not carry the preconceived charm of Paris. Most of the metros on the outskirts of Paris or near popular tourist areas give warnings against pickpockets and other petty theft. It is important to remember that crime does exist in the city; it is just not as widespread as it is in other places.