Megalodon was a massive predatory shark that dwarfed even the largest great white. The largest specimen reached lengths of 60 feet, and they routinely ate whales and other large marine mammals.
Mainstream science says this massive shark went extinct thousands of years, but there are those who believe Megalodon still may exist today. Meg may have adapted and evolved over time, from a coastal hunter to a deep-water shark.
Or, it may simply live in areas that humans do not frequent.
There are several accounts of very large sharks harassing boats over the past hundred years or so, but nothing that definitively can tell us is the Megalodon is still out there or not. The ocean is such a vast place, and it is conceivable that many large creatures exist out there that are still to be discovered.
The existence of Megalodon is a frightening possibility. If it decided humans were a food source no beach or small boat in the world would be safe from this massive monster.