Check-washing
Check-washing: erasing the ink on checks and changing themCory Doctorow: Bruce Schneier reports on the reputed practice of "check-washing" wherein fraudsters use solvents to take the ink off checks and then re-address them and change the sums on them:
If you are a ballpoint pen lover, switch to black ink when security is important. Among water-based inks, remember that gels are the most impervious. But when you're writing checks to pay the monthly bills, only one type of ink, the kind in gel pens, has been found to be counterfeit proof to acetone or any other chemical used in "check washing." Most ballpoint and marker inks are dye based, meaning that the pigments are dissolved in the ink.