The original team realized that introducing this technology into the commercial market could disrupt the status quo of traditional backup systems, which restore failed servers over a day or more.

FORBES: Tech CEO Shows How to Disrupt a Giant

They said the problem was that it then transmitted all the contained phone numbers to its servers, and failed to delete those belonging to people who had not signed up to the service.

BBC: Whatsapp

And it says BT failed to license a system used to let computer servers prioritise data - an IBM invention now owned by the search firm.

BBC: BT Tower