Short codes are convenient for banks and shops and expensive for you. Here is how they are billed.
What short codes are
Four- and five-digit numbers are not phone numbers in the usual sense: they are used for messaging and, rarely, for voice menus. They are rented by companies from aggregators, which is why the same short code can serve different services over time.
Free and paid
Incoming messages from a short code are usually free. Outgoing messages can be charged at a premium rate that is many times the price of a normal SMS. A confirmation reply is a purchase.
The subscription trap
A typical scheme: a message asks you to reply with a word or to send a code to a short number. The reply activates a subscription with a monthly fee. The fee is small enough to go unnoticed, which is why these schemes survive.
How to protect yourself
- Never reply to a short-code message you did not initiate.
- Ask the operator to block premium content.
- Check the monthly bill for charges with a four-digit sender.
When short codes are legitimate
Bank confirmations, delivery notices and two-factor codes come from short codes too — but they never ask you to reply with anything. A message that asks for an action is the suspicious one.
See also: cutting SMS spending, fake bank SMS.