zapper. up in washington state, mike sniffs them out. >> so in this case, got two combos here. >> but in the restaurant's tax return? only one combo. >> this combo -- >> disappeared. >> is gone. >> zappers work like this. let's say you sell 100 pad thais. software on a simple memory stick plugged into the register can erase, zap any trace of, say, 50 of them. so, you keep the sales tax you collected on those vanished pad thai orders. plus, you save on other state and federal taxes because all that income just disappeared from your books. the irs told us zappers can be and are used in restaurants, bars, liquor stores, golf courses, movie theaters. cash transactions are easiest to erase. >> it's almost like tracks in the snow. and what happens after the tracks are made? the snow melts. >> reporter: no one knows just