As Coinbase's security team explains, the letters urge recipients to scan a QR code and enrol in a "Digital Asset Compliance Portal" before time runs out. Bear in mind that the criminals could easily vary these details from letter to letter. The scam site then asks victims to estimate how much value they have in their cryptocurrency wallets, with ranges up to "$100,000+". Perhaps a reason why a scam like this can work is that the IRS has been tightening cryptocurrency holders' requirement to report details of their digital assets on their tax returns. As a result, written communications between the IRS and holders of cryptocurrency have become more frequent.