Bluejacking is a practice of sending anonymous text messages to mobile users using Bluetooth. Phones that are Bluetooth-enabled can be tweaked to search for other handsets using it that will accept messages sent to them. However, a user can avoid these messages by setting their device to "invisible" or turn off Bluetooth when not using it. Bluetooth is a protocol that allows devices such as mobile phones and laptops to send data to other devices, without wires, over distances of about 30 feet.
Bluejacking is the sending of unsolicited messages over Bluetooth to Bluetooth-enabled devices such as mobile phones, PDAs or laptop computers, sending a vCard which typically contains a message in the name field to another bluetooth enabled device via the OBEX protocol. Bluetooth has a very limited range, usually around 10 metres on mobile phones, but laptops can reach up to 100 metres with powerful transmitters. The name originated with a user named ajack on esato.com. Jack was in a bank, searching for other BT enabled devices. When he found a Nokia 7650, he sent the owner a message saying "Buy Ericsson". He called it bluejacking, and it stuck ever since.