transient_feed is getting scary. Is it legit , have I been hacked?

Hello everyone,

I was cleaning my database and noticed a large amount of transient_feed entries in my wp_options table. These entries are accouting for 2Mo in my DB.

Several questions about these entries:
1 where do they come from?
2 why are they stored in my DB although none of my plugins or pages are transient_feed content?
3 Have i been hacked?
4 How do I get rid of these entries definitely and make sure they don’t come back?

Thanks a lot for your answers. I’m really getting scared with that issue!