Someone goes to claim $200 in cryptocurrency they earned. Minutes later, they discover that the $3,000 they had saved has disappeared...
They didn't download a virus. They didn't share their password. They didn't reveal their 12 recovery words, either.
What happened was different: they ended up granting permission that allowed a third party to transfer their assets.
This type of scam is known as a Wallet Drainer and combines social engineering, fraudulent websites, and legitimate smart contract functions.
Let’s see how it happens, step by step, with a concrete example.
STEP 1. THE POST THAT LURES THE VICTIM
It all starts with a social media post announcing a reward of, for example, 200 USDC for certain users.
The link leads to a page that imitates a crypto project. It has professional-looking images, a countdown timer, and a button that says: Claim reward....
The user visits, convinced they’re taking part in a promotion.
STEP 2. CONNECTING THE WALLET
The page asks them to connect a wallet, such as MetaMask... The victim accepts.
At that point, the site can see their public address and check the assets they hold on the blockchain.
Let’s say it finds 3,000 USDC.
So far, connecting the wallet does not, by itself, authorize anyone to withdraw those funds. The danger comes in the next step.
STEP 3. THE APPROVAL DISGUISED AS VERIFICATION
To claim the supposed 200 USDC, the page asks the user to confirm a transaction.
The wallet displays an approval related to a smart contract.
The victim thinks they’re enabling receipt of the reward. However, the transaction may include a spending approval for their USDC.
Ethereum has a function called approve, which lets you set how much an authorized address or contract, known as the spender, can spend.
For example, the approval could allow the recipient to move up to 10,000 USDC.
The user only has 3,000, but the approved limit is higher.
They confirm the transaction, and it is recorded on the blockchain.
THIS IS WHERE THE CRITICAL MISTAKE HAPPENS: THEY DIDN’T AUTHORIZE RECEIVING A REWARD. THEY AUTHORIZED SOMEONE ELSE TO MOVE THEIR TOKENS.
STEP 4. THE DRAINER CARRIES OUT THE THEFT
Once the approval is confirmed, the malicious system can detect that it now has a valid authorization.
The attacker, or a contract they control with the necessary permissions, uses another function called transferFrom.
What is it for?
To transfer tokens from a wallet that previously approved that spending.
In our example, 3,000 USDC are transferred from the victim’s wallet to an address controlled by the criminals.
The victim doesn’t need to confirm that transfer again... The earlier approval allows it to happen.
When the transaction is confirmed on the network, the tokens change hands.
STEP 5. THE USER DISCOVERS WHAT HAPPENED
The page may show an error, keep loading, or simply fail to deliver any reward.
The victim checks their wallet again and finds that their 3,000 USDC have disappeared.
What’s most unsettling is that the approval could remain active if it still has spending capacity available.
If they receive more USDC later, those funds could also be exposed.
But one important clarification: approving USDC does not automatically mean approving ETH, Bitcoin, or all other assets. Each approval has a specific scope.
WHAT ABOUT SIGNATURES THAT DON’T REQUIRE PAYING FEES?
There’s another variant that uses mechanisms such as permit or Permit2.
Under certain conditions, the criminal can obtain a cryptographic signature off the blockchain and use it later to execute an authorized transfer.
This makes certain signature requests that look like simple verifications especially dangerous.
Not all signatures allow funds to be moved. Their contents and the permissions involved are what matter.
HOW CAN YOU AVOID IT?
Before confirming, check which token is being approved, which address will receive the permission, and what the spending limit is.
Never grant unlimited approvals to apps you don’t know.
Review existing approvals using tools such as Revoke.cash or MetaMask Portfolio. If you find suspicious permissions, revoke them as soon as possible.
Disconnecting a website from your wallet is not the same as revoking its permissions. And revoking an approval won’t recover money that has already been transferred.
🧠 This... Is simple....
The Crypto Drainer shows that a transaction can be technically valid and, at the same time, be part of a scam.
The blockchain records that an address granted permission. That alone cannot determine whether its owner truly understood what they were authorizing.
The criminal takes advantage of precisely that difference.
The victim thinks they’re clicking to receive money. In reality, they may be authorizing the mechanism that will let someone take it from them.
And by the time they understand the difference, the transfer may already have been executed and the funds may be out of their control....
🎥 Want more crazy tips to protect yourself ??? Then SUBSCRIBE!
