Virgin Media has apologised after some of its customers received hundreds of unwanted emails because of a distribution list error.
Anyone clicking "reply all" to a recent customer services email was able to message everyone on the mailing list.
The email was sent to inform customers of changes to Google services.
A spokesman said Virgin was "investigating exactly what has happened", and the company confirmed no more replies were able to be sent.
Virgin Media said the problem related to a "sub set" of its virgin.net email customers, but it did not know the precise number affected.
Although customers' addresses were not themselves shared, anyone pressing "reply all" and entering into the email chain exposed their own details to thousands of others - and the company urged people not to do so.
Some people reported receiving hundreds of emails, including spam messages and light-hearted exchanges between other customers.
Bob Alexander, from Taunton, said he had suffered "a great deal of inconvenience and stress" after receiving more than 700 emails.
The 69-year-old told the BBC: "I am a quadriplegic and to delete 700 emails from my Blackberry handset has taken me all evening."
Virgin Media later said it had resolved the problem, which it said affected "a small proportion of our customers".
The initial email had been sent by one of the company's suppliers, the spokesman said.
He added: "We apologise for the inconvenience caused."