Rory Cellan-Jones, a technical reporter for the BBC, said on Radio 4 that the websites were attacked using a distributed denial of service (DDoS).
He said that the BBC was regularly attacked by hackers but had means to tweak its site to recover from the attack.
The attack not only affected the maun BBC web site but also its iPlayer TV and iPlayer radio app.
The attacks started happening around 7AM today, but by 10.30AM everything was working normally again.
No one has claimed responsibility for the attack, and Cellan-Jones said the BBC hadn’t received cash demands from the perpetrator or perpetrators.