The 29-year-old was stopped at Luton airport on Wednesday by officers from the National Crime Agency (NCA), in a joint operation with the German federal police.
In November a major internet outage affected Deutsche Telekom customers, numbering more than one million according to German police.
At the time Germany’s Federal Office for Information Security said the outage was part of a worldwide attack on internet routers that exploited unsecured maintenance ports.
Following the arrest, Cologne public prosecutor Dr Daniel Vollmert said police hoped to extradite the man to Germany, where he could face a charge of attempted computer sabotage. The offence carries a prison sentence of up to 10 years.
Dr Vollmert told the Press Association: “He is accused of being the mastermind behind the attack.”
An NCA spokesman said: “NCA officers arrested a man in his twenties at Luton airport on February 22 2017 under an EAW (European Arrest Warrant), on behalf of the German federal criminal police office (BKA) in connection to offences committed in Germany.”
He said the man was arrested in connection to “separate offences committed in the UK” but could give no further detail.