A collection of large-scale Bitcoin owners—known as whales—have moved 94,504 bitcoins, worth over $1 billion, to an unknown wallet. That’s over 0.5 percent of all coins in circulation, making the recipient the owner of the fifth richest Bitcoin wallet in existence.

The bitcoins were sent to a single wallet at 3am UTC this morning from 15 addresses. Over half of the bitcoins, 53,000 of them, came from a single address.

The transaction saw the price of Bitcoin spike from $10,569 to $10,790 in a matter of hours.

Nobody has claimed ownership over the wallet, and speculations vary.

We don’t have much to go on, apart from the fact that the transaction fee was high—some $700—which suggests that they wanted to confirm the transaction quickly, perhaps for security reasons. Or that the transaction had a lot of inputs that each have their own minimum fee; this is where multiple chunks of Bitcoin are brought together in one transaction.

Some say the wallets could be owned by Bakkt, which started offering its own bitcoin custody service today, Bakkt Warehouse.

Or perhaps it’s an exchange consolidating its holdings. Most of the top ten wallets by holding volume are known to be associated with an exchange whereas this one isn’t—but that doesn’t necessarily mean that it isn’t an exchange. We just don’t have proof that it is.

It could even be the fallout of the alleged Chinese Ponzi scheme PlusToken, which has been accused of making off with $3 billion worth of customer funds.

One thing, however, is certain, these secret whale movements are becoming more common. Less than two weeks ago, someone moved around 77,000 BTC, around $780 million, into three unknown wallets. Do they know something we don’t?