Half life has been run on many many office lans
...we used to play most Friday afternoons when the bosses were in 'meetings'.
If you walked around the fairly small office (200 people, 1 floor), amongst the excel and word sheets you occasionally see someone playing half life. A few in accounting, a few in IT, a few in comms...
It was a government quango so its not like we had to make any money anyway, just make sure a website never went down. And given the boring industry nature of it, no-one would notice if it did anyway...