Most euro cylinders have a weak spot where the tread for the fixing screw is. You can easily break the lock by fatiguing the metal until it snaps.

There are ways to protect against this, with p. ex. hardened insterts that hold the lock together.

Professionals use a tool called a Cylinder Cracker for this purpose. The adjustable clamp adaptor, which features a profile on the inside, grips the cylinder and easily breaks it, even if there's very little overhead (only approximately 2 mm required for high-quality tools) to grab onto.