Due to the decentralized nature of the blockchain that Bitcoin uses, all transactions can be viewed transparently, either by having a personal node or by using blockchain explorers that allow anyone to see the transactions happening live. Each node has its own chain copy, which is updated as new blocks are confirmed and added. If you want, you can follow Bitcoin wherever it goes. For example, Bitcoin exchanges have been cheated by hackers in the past, and those who keep Bitcoin in the stock exchange lost their assets. Although the hacker is completely anonymous, the Bitcoins they issue can be easily tracked. If Bitcoins stolen in some of these attacks were to be moved or spent somewhere, these transactions would have been known.