The UK's National Crime Agency (NCA) has arrested a suspect at one of London's airports in connection with November's cyber attack on Deutsche Telekom.
The 29-year-old Briton was arrested on Wednesday in response to a European arrest warrant.
The cyber attack targeted the routers of 900,000 Deutsche Telekom customers leading to internet outages for around 4.5 per cent of the German firm's customers.
The NCA said the person was being held by police in the UK prior to an extradition hearing expected to take place at Westminster magistrates court either tomorrow or Monday.
The attack followed a Deutsche Telekom databank malfunction in June that led to millions of its mobile customers losing their connection.