Ex-News International chief executive Rebekah Brooks has been arrested by police investigating phone hacking and bribery at the News of the World.
The 43-year-old was arrested by appointment at a London police station and remains in custody.
She was arrested on suspicion of conspiring to intercept communications and on suspicion of corruption.
She quit News International on Friday as pressure mounted over her role in the deepening scandal.
Mrs Brooks was editor of the paper between 2000 and 2003, during which time the phone belonging to murdered schoolgirl Milly Dowler was tampered with.
BBC Business Editor Robert Peston said News International was not aware that Mrs Brooks would be arrested when her resignation was being discussed at the company on Tuesday and Wednesday of last week. She eventually resigned on Friday.