Apologies if already covered on previous threads, but I noticed this recently and thought others should know:
I have an i phone and i pad, both registered to me. Scanning adultwork on my i phone, as usual, in the back room.
Missus on i Pad in the other room. She makes a cuppa, I pick up i Pad, notice with horror my search history now showing on i Pad!!
Did a speed clean of History, through Settings etc. Got away with it...
i Cloud syncs your music, mail, Safari etc between any Apple devices
Did a bit of research and this can be rectified in Settings / i Cloud/then turn off Safari.
I am normally very very careful with devices and delete histories, cookies the lot all the time, but this nearly caught me out.
Hope this helps..