This happens a lot at work, and I don't think there's a single word for it - or is there?
- Browsing the web for content unrelated to work
- Taking company time for personal grooming (like painting nails, shaving, etc.)
- Using the company refrigerator to temporarily store one's groceries purchased at lunch.
- Printing stuff not related to work (worse yet, if it's material for employment somewhere else.)
Stealing is not specific enough.