In a story on last week's atrocities in Madrid, Reuters writes:

Thursday's death toll was the biggest in a guerrilla attack in Europe since December 1988 when a bomb exploded on board a Pan American Boeing 747, bringing it down on the Scottish town of Lockerbie. In all, 270 people died.

According to Reuters, the bombing of Pan Am Flight 103 was a guerrilla attack. Now, for some, it may be hard to draw the line between terrorism and guerrilla warfare. But is this such a difficult case?