People other than the ones you agreed to let monitor you, well, monitoring you. Also, it's a major risk to the company itself, who knows what can be read off of employees screens if they're compromised.
Yeah, it seemed far fetched to me at first but I guess surveillance might be useful to a 3rd party. I read an article a while back on how people make equity trades based on data found through satellite images of refinery tanks and whatnot. I guess unsecured internal surveillance cameras could allow an outsider to find out if a company was really busy or just faking it.
