Investors who held large amounts of bitcoin (BTC) and didn’t move their coins for years are suddenly showing signs of life, sparking conversations on Crypto Twitter about the possible reasons behind the activity.

The investors are known as “whales” because they hold large amounts of tokens in their digital wallets. They can influence the price or sentiment around a token because of the size of their holdings.

One such wallet, which was last active in 2012, moved more than 400 bitcoins ($11 million) over the weekend, data shows. The bitcoin whale moved 360 bitcoins to one wallet and 40 bitcoins to other wallets. The whale had purchased 900 bitcoins in 2012, holding onto the asset ever since then, with a nearly 40,000% gain on the initial investment.

The movement comes on the back of several other whales moving large quantities of bitcoin and ether (ETH) in the past few weeks.

Another whale wallet moved 279 bitcoins earlier in April after over 10 years of inactivity. The whale received 1,128 bitcoins between 2012 and 2013 when the price fluctuated between $12 and $195. The holdings are now worth $31 million.

Ether holders are moving their tokens, too. Last week, a participant in the ether initial coin offering moved 1 ether to another wallet after eight years of inactivity. The wallet holds more than 2,356 ether purchased at 31 cents apiece in the ICO. It’s now valued at over $4 million.

The identities of these whales are unknown, and none of them has said publicly why they are making the moves.

The silence has spurred speculation on Crypto Twitter, with possible reasons ranging from developers of the dark web site Silk Road getting access to the whales’ wallets to insiders in the know moving tokens ahead of bad news. Some have speculated that the holders’ wallet passwords have been cracked.

“We’re now at waay too many 10+ year wallets springing to life on multiple assets all of a sudden,” crypto investor Adam Cochran said on Twitter. “Unless these wallets are somehow related to Mt Gox cold storage, then some old wallet generator has to have been cracked.”

Mt. Gox, which was once the largest bitcoin exchange in the world, closed shop in 2014 after it was revealed that it lost hundreds of thousands of bitcoin.

Cochran’s reasoning may be plausible, because old wallets have repeatedly been the target for hackers and online thieves.

Earlier this month, Taylor Monahan, founder of MyCrypto, a wallet manger for ether, flagged a massive “wallet draining operation” that seemed to affect whales and early holders of ether.

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Monahan estimated more than 5,000 ether were drained from such wallets in the sophisticated attack. “My best guess is that someone has got themselves a fatty cache of data from 1 plus yr ago & is methodically draining the keys as they parse them from the treasure trove,” Monahan tweeted at the time.