A recently found Facebook bug lets you post un-deletable messages to friends’ walls. Here’s how it works: Once you’ve blocked a person on Facebook, he or she can no longer see content you’ve posted on the social network, including posts you’ve made to their own wall. Since the content is no longer visible, it can’t be deleted. The only way either party can see the post again is if the block is removed. In a way, Facebook lets you know that’s going to happen when you block someone in the first place. Read the full story at Mashable.