It is a safe assumption that most desk job workers (let alone most of society) do not have proper posture all day long. For most, it takes a conscious effort to maintain good posture at all. Constant hunching over and leaning can cause major aches in your back which will last far longer than the desk you are sitting at. Right now, while reading this, I bet you are adjusting your position in your chair.
While it is unavoidable to slip every now and then, you can follow a few simple tips to ensure you are maintaining good posture more often than not. The simplest way is to utilize props – a lumbar support pillow for your lower back, an alarm to make you get out of the chair and move every 30-60 minutes at work, post pictures of proper posture at your desk, etc. This article gives some other suggestions to maintaining proper posture for a desk job – although good posture is important for everyone!
If the damage is already done, try yoga to correct your spine damage caused by your desk job. Yoga is a low-to-no impact stretching exercise that will help get your muscles in gear to make good posture even easier from day to day. By working your muscles regularly, it will be easier to maintain good posture because your muscles will do most of the work for you!