The Financial Times website, FT.com, was struggling to cope Thursday after the theft of equipment at a hosting center, which is believed to have been unmanned.
The online shopping site of Sainsbury's was also affected, by the theft. Optical wiring, routers, servers and switches were removed from the site by thieves, who police believe were after scrap metal.
The FT has been unable to publish new articles or update data on its site, following the thefts which took place at a Cable & Wireless network site, near to one of its data centers in Watford, north of London.
Instead, the FT.com site was being run on backup facilities in the United States.
By mid afternoon the site was fully restored. A company representative said, "There was a reduced FT.com service on 10 July due to equipment being stolen over night from our third party hosted data center site. Full functionality has now been restored and we would like to apologise for any inconvenience caused to our customers and readers. "
Salisbury's, meanwhile had to cope with the second major outage on its shopping site in a month. A message apologised to customers who "are unable to get access to our groceries site at the moment. This is due to a technical problem that our internet providers, Cable & Wireless, are experiencing."
Sainbury's was able to carry on deliveries as usual and its site was restored Thursday afternoon.
Cable and Wireless itself was tight lipped about the break in. The hoster would not confirm which of its customers were affected or how the theft occurred.
A representative said "Cable & Wireless are experiencing some network issues due to the loss of a number of servers following a break-in at our site in Watford. This being investigated and is now a police matter.
"We have employed a specialist engineer to minimize the loss to our customers. We can't comment on individual customers."
Earlier this year, Norwich Union signed a £300 million, six year deal with Cable & Wireless. In 2006 Cable & Wireless signed a contract to provide the new Police National Network (PNN3) in a deal worth £75 million over five years.