Walking ATM refers to an illegal immigrant or migrant worker who isfrequently robbed because they have no bank account and so must carry all theircash. They are afraid to leave the money where they live because they may besharing an apartment with a dozen or so others.

“移动提款机”指经常被抢劫的非法移民或农民工，他们没有银行账户，所以只能把钱都带在身上。他们也不敢把钱放在住的地方，因为他们通常都跟好几个人共住一套房子。如何考托福

Since many undocumented immigrants are unable to open bank accounts, theyare often forced to carry large amounts of cash, making them susceptible tocrimes of robbery or theft.

因为很多没有合法身份的移民都没办法到银行开户，所以经常不得不把大量现金带在身上，由此很容易成为抢劫和盗窃的受害者。