Spoilers for the trailer of Silicon Valley’s season finale.

Tonight’s Silicon Valley season finale is titled “Fifty-One Percent,” and according to the trailer for the episode, it features a crazy twist centered on what’s called a 51 percent attack. This is when an organized group of cryptocurrency miners achieve a majority on a blockchain network, which enables them to hold the network hostage and disrupt it in various ways. On the show, Pied Piper’s enemies start joining the blockchain network until they reach a 51 percent consensus, which gives them the power to “delete all of our users, all of our developer apps, crash our coin. This would be the end of Pied Piper,” explains Dinesh.

The 51 percent attack does exist in the real world and has been deployed against smaller coins like Krypton and Shift, which are clones of the more popular cryptocurrency Ethereum. Both were attacked by the same group, which calls itself the 51 Crew. Once the group held a majority of both coins, it then sent their creators a ransom note, stating that serious damage would occur to Krypton and Shift if they weren’t paid. This is a real threat; a group of coin miners that control more than 50 percent of the network can wreak havoc by stopping payments between users, or reverse certain completed transactions, so that it would look as if they still had the coins they spent.

For smaller coins in particular, rewriting transactions on the public ledger can be damaging because it ruins the legitimacy of all transactions — something that could very well kill the coin. It’s a problem that doesn’t have an exact solution because such miners are taking advantage of the decentralized way the network is built.

But Cornell cryptographer Emin Gün Sirer tells The Verge that 51 percent attacks can’t do quite as much damage as the Silicon Valley episode suggests. While messing with a coin like this might crash it, it wouldn’t allow attackers to “delete all of our users, all of our developer apps” as Dinesh suggests.

“Miners at 51 percent or more have a lot of powers, but they do not have the ability to change the actual rules of the system, nor can they usurp funds,” Sirer explains, “They can rewrite the existing blockchain in a limited fashion: they cannot introduce transactions that don’t already exist, they can omit any transaction that they want, and they certainly cannot change any of the existing rules.”

Sirer suggests that the exaggerated power attributed to the attack are just a bit of dramatic license. “Sometimes, for a good screenplay, Hollywood will take liberties with the technical facts on the ground. I think we have one of those situations here.” Silicon Valley has a long history of raising real issues in the tech community, though sometimes exaggerated for effect. Last week, its penultimate episode highlighted excellent points about Bitcoin, and even though this week’s episode is a little less accurate, it still points out a significant concern. The 51 percent attack isn’t extremely well-known outside of the cryptocurrency researcher community and it does suggest a potentially serious flaw in completely decentralized networks. For people trying to do business on those blockchains, it’s a problem worth acknowledging.