REUTERS/Pichi Chuang
The British broadband and telephone provider's website was hacked, putting up to 4 million customers' data at risk, the company said.
On Monday, Northern Irish police subsequently arrested a teenager in County Antrim, Northern Ireland, on suspicion of offences relating to the Computer Misuse Act.
A spokesperson for the Police Service of Northern Ireland told Sky News that "the investigation being conducted by the Metropolitan Police Cyber Crime Unit, Police Service of Northern Ireland and National Crime Agency is continuing."
TalkTalk says it has received a ransom note from someone claiming to be the hacker following the attack, which reportedly demanded £80,000 in bitcoin.