How some federal employees are pretending to work using 'mouse jigglers'.
FTFY.
This happens everywhere that managers are more interested in warming chairs than actually being productive:
If you measure your employees by their work done, this isn't an issue; if they're getting what you think should be eight hours of work done in four, you promote them, pay them more and/or give them more responsibilities.
If you measure them by the percentage of hours they spend warming a chair, they'll...warm the chair.