How do hackers do this, by guessing easy passwords or by other means?

Keyloggers or other spyware could do it, and an insider compromising the password is also plausible - say, a fired employee with an axe to grind, or someone foolishly emailing it in clear text. The password may have been weak to begin with, and guessable.

Another alternative is that there was no hack at all, and these were simply sent unauthorized by someone who had the password. Given that a major newspaper headline can (and in this case, did) move markets significantly, there's a major financial incentive to place a highly leveraged bet, put out the "hacked" tweet, cash in, then falsely claim hacking.

How do they know? If it were any other publication, I'd be concerned! Sure it isn't an inside job, New York Post?

P.S. Speaking of publications, the The Twelfth Annual "You Call This NEWS?" Awards have been posted.


rocktivity

The Pope believes that World War Three had already begun. But unlike WWI and WWII that happened all at once, the current war is happening in stages - this he said during a private meeting with a congregation of Jewish leaders headed by Ronald S. Lauder on Sept 17 at Pope's house in Santa Marta.

http://au.ibtimes.com/articles/567003/20140922/pope-francis-meets-jews-believes-wwiii-world.htm#.VLljHXtiS7Y

Just like we see today, there were plenty of prior geopolitical events that set the table for the main course.

Check out the prior events that set the stage in the first: https://en.wikipedia.org/wiki/Causes_of_World_War_I