A brief explanation why…
Discovered by Kaspersky in June 2004 and purportedly nicknamed after employee Elena Kabirova, the Cabir worm was designed to target Series 60 Nokia phones running SymbianOS and it used the handset's Bluetooth connectivity to send itself to all Bluetooth-enabled devices (including those not running Symbian, such as desktops or printers).
Also known as Caribe, SybmOS/Cabir, and other names, the malware required someone to accept it as a file transfer and in some instances it would keep displaying prompts until you were forced to agree.
Fortunately, the worm wasn't released into the wild and was instead sent to antivirus companies who concluded that it seemed harmless in its current state and was created a group of hackers known as 29A as a proof of concept for attention.
Later, a Cabir variant known as Mabir emerged with the ability to spread over Bluetooth as well as MMS by sending a .sis file over cellular networks.