Broadband connections in east London were hit when thieves broke into BT's Commercial Road telephone exchange.
The burglars gained entry to the facility in Stepney Green at around 03:45 BST yesterday (Thursday, September 25th) morning, taking network cards and other equipment.
Three areas were left without broadband connections until around 14:00 in the afternoon.
Detectives from the Metropolitan Police are said to be working with BT engineers to quantify the losses of network gear.
No arrests have yet been made.
The news follows a break-in at BT's Mayfair telephone exchange earlier in the month, when thieves took over £2 million worth of equipment while Madonna and her husband Guy Ritchie threw a party in a pub next door.
Police have declined to speculate on whether the two incidents could be connected.