Broadband customers of TalkTalk and the Post Office have experienced outages due to a possible cyber attack.
The Post Office has been affected by problems impacting around 100,000 of its customers since 27 November, a spokeswoman told the BBC.
TalkTalk customers have also been affected by problems, the BBC reported.
The problem may be the same as one which affected Deutsche Telekom customers in Germany recently.
Deutsche Telekom customers were hit on 27 and 28 November 2016, with over 900,000 customers experiencing internet and telephony failures, or nearly 5 percent of users.
According to the BSI, the failure was due to a worldwide attack on selected remote management ports of DSL routers in order to infect them with malicious software.
The malware, Mirai, is encoded with a list of default passwords and trawls the net, looking for passive internet-connected devices such as routers and camera. It inputs these passwords into the devices to try and take them over.
Sophos wrote in its Naked Security blog that the most likely outcome was that the Mirai software had been deployed to take over the routers to co-opt them into the botnet.
Since the devices were not susceptible to being taken over by Mirai, they caused the router to be cut off from the internet, “unable to pass traffic in either direction and possibly unable to reconnect to the internet until it is rebooted.”
Whether the same has occurred in the case of TalkTalk and the Post Office is unclear.