There was recently a Twitter app called Samaritans Radar which supposedly would scan your friends’ tweets (without their knowledge or permission) for keywords suggesting that they might be suicidal, and then it would send you an email suggesting that you contact them and check that they were ok. There was a HUGE scandal about this app – first that it was totally useless at doing what it promised to do, and second that it was funded by a UK government organisation whose interests are “terrorism, cyber-security and surveillance”.
Following a massive backlash against it, it was removed within a couple of weeks but they still refuse to admit who was collecting the data for it.
My theory is that it was searching for other keywords in secret, pertaining to terrorism, and the suicide thing was only a ploy to get people to download it.
I wrote a blog thing about it here: http://justafewordinarywords.wordpress.com/2014/11/07/samaritans-radar-who-spies-on-whom/