Every age has had its paranoia, I imagine. After all, the world does have its dangers and among them are indeed some of the people who have risen to power — who themselves get paranoid about challenges to their power. In relatively recent memory there was the destructive McCarthy period in the US and later, Nixon's creepy fears. Closer to home, not too long ago the RCMP kept files on just about everyone who jaywalked, and hippies were certain their phones were tapped and flushed their dope down the toilet whenever there was an unexpected knock on the door.
Now, of course, it's American reaction to September 11 that's the music behind our current pas de paranoia. And now, too, there's a whole lot more than just phones to "tap", much of it right out there in the open as we fling our lives into the ether with little caution or taste. So it should come as no surprise that the US Department of Homeland Security monitors this gush on the social media. The Electronic Privacy Information Center (EPIC) tracks the trackers whenever it can and has in fact brought suit against the Department of Homeland Security under the US Freedom of Information Act to compel it to disgorge records about its monitoring activities.
As part of that lawsuit, EPIC has recently obtained the DHS 2011 "National Operations Center Media Monitoring Capability Desktop Reference Binder" [PDF] (lightly "redacted"). It's a bureaucratic manual, too boring to go through in detail here. But it's worth having a look at the section that lists the trigger words DHS monitors social media for, terms, in the language of the manual "to provide situational awareness and establish a common operating picture."
Interestingly, the document coughed up by the DHS is a graphic image PDF, so that you can't copy the text. However, a website called Animal has gone to the trouble of turning the list into text, which enables me to tell you that there are 377 trigger words. Some simply relate to natural disasters—tsunami, tremor, storm etc. And others are clearly related to DHS's anti-terrorism work—terrorism, weapon's grade, IRA etc. But many are "innocent" words, at least taken by themselves or in otherwise innocuous contexts—recall, public health, swine, airport, cops, deaths, incident etc.
One imagines (but, alas, with wavering confidence) that there is a stage in which some sensible judgment is applied to whatever the day's trawl brings up. Can't say I'd like to be one of the people who have to sort through the mess.
A last note on the title to this post. It's a line from a folk song from at least the 1920s and maybe earlier. And though the song has had its revivals in times of acute public paranoia, it likely referred originally to the one great power from which no one could hide, namely death. (See this forum discussion, if you're interested in such things.) The great Leadbelly sang it, and you can listen to him tell you here about what's coming your way, no matter which words you're careful to avoid.