Quora: Why do ATMs return cards so slowly?

So, it’s not to annoy you, but to annoy the fraudsters

Answer by Rahul Keerthi:

It’s intentional: not slow, but jittery. The jitter is to reduce the probability of simple ATM skimming.

Firstly, it’s useful to understand how simple ATM skimming works.

1. Skimmers are after two things: the data on your card’s magnetic stripe (magstripe – it’s like cassette tape fastened to the back of your card) and your personal identification number (PIN)
2. They use gadgets that can be attached to or placed over the ATM card reader slot that will read and copy the magstripe data as the card is ejected from the machine
3. They may also use hidden cameras or other ploys (shoulder surfing, for example) to see your PIN as you enter it
4. They can then replicate your card and using your PIN, withdraw money from your account

[Image credit: Baltimore Sun]

Mind you, this is simple ATM skimming. More advanced techniques exist, some that aren’t yet figured out even.

What jitter does is foil the process of reading the magstripe data. ATM skimming devices typically prefer ejection to insertion as the card is machine-rolled out (as opposed to hand-fed in) and so, smoothly, evenly passed through the slot.

Jitter provides a simple physical solution to this potential problem: it introduces jitter into the ejection of the card from the reader.

This stop-start motion distorts any data read from the magnetic stripe on the card, making the copied information unusable.

Unfortunately this technology isn’t fool-proof, but it is a first deterrent that almost every major ATM vendor (i.e. NCR Corp., Diebold, Fujitsu and Wincor Nixdorf AG) employs – hence the ubiquitous “slow” returning of ATM cards that we all experience.