If aliens with giant ships were actually invading planet Earth, you can be pretty darned sure you would hear about it within a matter of minutes (thanks, Twitter). With that in mind, anytime you see a video or a picture of a supposed UFO flying near planet Earth, just remember that it's probably a hoax. Of course, even if it is a hoax, it can still be pretty cool to check out what others are presenting as "evidence."
Take, for example, the following (clearly fake) video of an alien "tripod" walking around the city of Novosibirsk in Russia. As Novosibirsk is the third most populous city in Russia, you can be sure that if this was actually happening, we would have at least seen one terrified tweet about it.
It's still pretty cool to imagine it happening, though.
(source: World Truth)
When the aliens do invade, I can assure you that we'll all be gone faster than we can blink. So savor these fictitious invasion scenarios in which we actually stand a chance against our new overlords.