A purge of unregistered cable modems by Virgin Media, part of a records clean-up, has left hundreds of customers without internet access for up to 10 days.
The programme has been running without problems since February, but in the last two weeks has hit active customers using old hardware.
Virgin Media has been trawling its databases of MAC addresses for devices not matched to registered accounts. A technical glitch caused modems issued by NTL to be frozen out of the network.
Customers wrongly affected by the purge should call customer services to have their modem manually restored to the database. Some have been sent new modems.
A Virgin Media spokesman apologised for the errors and said today: "The vast majority of affected modems were end of life or no longer in service due to disconnected accounts.
"A small percentage of unregistered modems were in use by customers, however due to incomplete records inherited from previous guises of the company, identifying these customers was impossible. The process to reactivate valid customer modems had been running smoothly until about a week ago, when a technical issue meant re-activation was delayed."
He said the technical glitch has been resolved and that staff are working through the backlog of customers disconnected in error.
Customers had speculated that the programme was part of efforts to battle illegal modem cloners, but the firm denied this, saying it merely aimed to spruce its records. ®