hear about (someone or something)
To learn about someone or something, typically (but not always) via word of mouth. Wow, I'd heard about your injury from your mom, but I didn't realize it was so grisly. Did you hear about Jade? She was in a car accident and broke her leg in three places. That website gave me a survey, asking me how I heard about it.
hear about someone or something
to learn about someone or something. (Not necessarily by hearing.) Have you heard about Tom and what happened to him? I heard about the accident.