The Money Tree Scam
Money trees are wonderful objects in Second Life used to welcome newcomers and provide them with some extra spending money when they fall short, since most 'newbies' do not have the means to earn cash any other way until they become comfortable with a trade. These operate on donations, which is then converted into objects shaped like dollars that spawn on the trees. When clicked, they grant you small amounts of Linden dollars. Usually about $L1 per object. However, this wonderful feature in the world has and can be exploited. Those who do this, however, face serious consequences.
The scam works like this: In order to donate to the tree, a generous soul must right click on and use the radial option "Pay..." to an object attached to the tree, which is a small decorative post. One Resident of Second Life created an invisible, payable box around the donate post. When users would go to pay donations to the post, they were actually donating to the scammer, who gets rich from generous people trying to assist newbies. This scam can be detected, and rather easily. If there is suspicion as to where the donations are going, one can simply use the View menu to activate an option called "Show transparent objects", which highlights all invisible objects as a shade of transparent red. If there is a red box covering the post, then it has been covered with a different object and is likely being scammed. If you stumble upon such a thing, be sure to report it, to the landowner or a Linden Labs representative.
The creator of this scam has apologized and removed the scam boxes. However, considering the relative simplicity of the scam, it is likely copycats could replicate the scam. Keep in mind that it is a near certainty that those donating to the trees are veteran residents of Second Life, and will be quick to notice any such scam, seeing as it is just as easy to notice as it is to copy.
This scam is part of a larger class of scams known as the invisiprim scam, or caging. Any store that allows public building can fall prey to this, with invisiprims set over their vendors or ATM devices.