Four people have been arrested by police investigating the cyber-attacks that have caused havoc at M&S and the Co-op.
The National Crime Agency (NCA) says a 20-year-old woman was arrested in Staffordshire, and three males – aged between 17 and 19 – were detained in London and the West Midlands.
They were apprehended on suspicion of Computer Misuse Act offences, blackmail, money laundering and participating in the activities of an organised crime group.
All four were arrested at their homes in the early hours of Thursday. Electronic devices were also seized by the police.
One of the suspects – a 19-year-old man – is from Latvia, the rest are from the UK.
Neighbours described a large police operation in the quiet Staffordshire cul-de-sac where the 20-year-old was arrested.
They said dozens of NCA officers, some wearing balaclavas, arrived in the early hours of this morning and smashed down the door of a family home. Later they were seen taking away a large number of electronic devices.
Paul Foster, head of the NCA’s National Cyber Crime Unit, said the arrests were a “significant step” in its investigation.
“But our work continues, alongside partners in the UK and overseas, to ensure those responsible are identified and brought to justice,” he added.
