I was intrigued by a scam which consists in revealing its mnemonic phrase on a forum, on twitter or other.
So I installed one of this wallet which indeed has funds. I observed what was happening and asked for explanations (to a bitcointalker): there are erc20 tokens in a wallet for example, but to transfer them you need fees. The people who install this fraudulent wallet send the fees which are instantly scanned and sent to another wallet. This is really very clever.
I would like to understand better how it works. From what I understood, the scammers use some kind of robot to instantly send the fees elsewhere.