Some people are brazen. I knew someone who daytraded at the office. They only daytraded, didn't do any of their work. The boss didn't want to deal with severance, so had IT get creative. This was before smartphones, so the someone either traded on their home computer, or their work desktop machine. If his machine tried to go to his brokerage firm (i.e. etrade.com) it would instead go to a different website. Someone gave notice pretty quickly. If I remember correctly, boss was petty and was going to make him stay the whole two weeks in the office. Someone changed their resignation to "effective immediately" after that.