In ancient Greece (469 - 399 BC), Socrates was widely lauded for his wisdom.
One day the great philosopher came upon an acquaintance who ran up to him excitedly and said, "Socrates, do you know what I just heard about one of your students?"

"Wait a moment," Socrates replied. "Before you tell me I'd like you to pass a little test. It's called the Triple Filter Test."

"Triple filter?"

"That's right," Socrates continued. "Before you talk to me about my student let's take a moment to filter what you're going to say. The first filter is Truth. Have you made absolutely sure that what you are about to tell me is true?"

"No," the man said, "actually I just heard about it."

"All right," said Socrates. "So you don't really know if it's true or not.
Now let's try the second filter, the filter of Goodness. Is what you are about to tell me about my student something good?"

"No, on the contrary ..."

"So," Socrates continued, "you want to tell me something bad about him, even though you're not certain it's true?" The man shrugged, a little embarrassed.
Socrates continued, "You may still pass the test though, because there is a third filter - the filter of Usefulness. Is what you want to tell me about my student going to be useful to me?"

"No, not really ..."

"Well," concluded Socrates , "if what you want to tell me is neither True nor Good nor even Useful, why tell it to me at all?"

The man was defeated and ashamed.
This is the reason Socrates was a great philosopher and held in such high esteem.

It also explains why he never found out that Plato was shagging his wife.

Keep this philosophy in mind the next time you either hear a rumour, or are about to forward one. The strategy is quite efficient, and this becomes evident when you are exposed to a rumour you already know is false. There are more things to add...

Follow up:

• Sometimes you've heard it elsewhere, and a couple of days later you hear it again, in a slightly modified form. This is how you can monitor the evolution of a rumour and see how it changes. My observations have shown that rumours tend to become more aggressive. If it was about a drunk person, we later find out the person was also taking drugs; and a couple of days afterwards we might hear about the person getting arrested for assaulting a policeman while being high and drunk.
• Sometimes you can tell that a rumour is a rumour because you know the actual event from which it was derived; or you are qualified enough to figure out it is absolutely impossible (ex: car mechanics can bust myths about a Lada driving at 400 km/h, computer tecchies know that you cannot hack a bank by clicking a shiny icon on a fully 3D desktop, like they do it in movies, etc). When you stumble upon it, you're shocked by how 'creative' and sick people's imagination can be.
• The easiest way to catch a rumour is when it is about yourself; someone has seen you in a certain place, with another person, talking about something, etc. Some people can make things up just for the fun of making things up, others may do it because they're planning to undermine your authority. Either way, a great number of rumour-forwarders readily available will help them spread their 'news' and establish a campaign against you. It happened to me a couple of times, I found out I was an idiot; and when I traced the information back to the source, I found a person I've never seen or have spoken to :-) Who the hell believed them in the first place?

Yeah, it is sad, but I have to admit that our society is powered by rumours, and many individuals naively talk about things without bothering to check them, demand proof, etc.

To help myself monitor these things easily, I do the following when I deal with known rumours or potential ones:

• When someone tells me about it, I ask them who the original source is, and who the source of the source is, and so on, until I find the starting point;
• I ask them if they bothered to verify the claims themselves, or if they asked their source if they attempted to do that;
• If they haven't tried that, and the rumour is obviously bogus - I conclude that the person can be easily manipulated, but
• If they did perform some basic backtracking and source-checking - I tell them they should always notify the receiver that the forwarded message is potential FUD.

In other words, these simple metrics can tell me whom I can trust more, and whom I can trust less. Moreover, it might be useful to know who can be manipulated and who cannot ;-)