Finnish data security firm Codenomicon says software faults in Bluetooth devices are becoming easier to exploit, putting users at risk.
Bluetooth radio technology is widely used to link cellphones to their accessories, and its security has not been considered a major problem.
Codenomicon, however, said in a research paper that it found critical problems in all Bluetooth-enabled car-kits it tested this year.
Bluetooth car-kits allow users to talk hands-free while they drive. Faulty security can give criminals access to information on users' phones, and coding errors could lead to damage to the car's electronic system and put drivers' safety at risk.
"The problems are in the implementation. Coders make human mistakes," technology chief Ari Takanen told Reuters on Friday, adding that deciding which device was more secure was very difficult.
"Quality of the software is rarely visible to consumers."
Bluetooth industry lobby Bluetooth SIG, when asked to comment on the findings, said the technology was secure.
"One of the reasons these members pick Bluetooth wireless technology is because of the strong security Bluetooth technology can provide through effective implementations by the OEMs (original equipment manufacturers) who build these products," said Mike Foley, Bluetooth SIG's executive director. (Reporting By Tarmo Virki; Editing by Jon Loades-Carter)