My least favorite machine is probably the torso twist machine. You sit on the machine and twist your upper body against resistance, while the lower body is still. The intention is to work the obliques (your waist muscles), however most of the rotation comes from the lumbar spine, causing compression on the discs. In fact, almost any exercise where your lower body is fixed and your upper body rotates (especially against resistance) puts stress on your spine. If you insist on using this machine, keep the weight very light and the reps few.
You will get a safer abdominal workout by doing cable (or resistance band) twists: Stand with your left side facing the pulley or band attachment, hold the band with two hands in front of your waist. Twist towards your right, allowing your torso (and hips) to move. Your left heel will come up as you twist. This is a safer and more useful exercise (think about hitting a tennis or golf ball), as your hips are designed to rotate with your spine.