* Islamist sect Boko Haram behind similar attacks
* Attacks continue in face of military crackdown
* Boko Haram biggest security threat in oil producer (Adds details, background, releads, changes headline)
By Lanre Ola and Ibrahim Mshelizza
MAIDUGURI, Nigeria Jan 14 (Reuters) - At least 17 people were killed on Tuesday in a car bomb in Nigeria's northeastern city of Maiduguri, the ...