A massive blunder has seen the sensitive personal details of 15,000 Hackney residents – including address, sexuality and rent accounts – leaked online.

Bungling council officers have also revealed the age and housing benefit entitlement of Hackney Homes tenants and leaseholders in the botched Freedom of Information request, which was inadvertently published in full on the website What Do They Know (WDTK).

The private information was publicly available online for 11 days before the error was noticed on November 25 – but affected residents were only informed of the huge data breach in a letter sent out this week.

Hackney Council insists that only 11 people viewed the document, and that the data would have only been accessible to people with “detailed” IT knowledge.

But the data remains in the hands of the person who requested the FOI, and residents affected said they have been left vulnerable and in fear of identity theft.

One victim, Alan Zeligson, described the incident as “shocking” and said: “The information that was available on the website may be sold on. Residents and leaseholders are at risk of having their identities stolen.”

Tim Abrahams, 48, a Hackney Homes resident in Homerton, said: “It just seems to me that they are completely incompetent. I would say that is a product of the failure of the organisation as a whole and that if any individuals are going to get fired, it should be somebody at the top.”

Henry Bulbrook, 52, said: “I thought the letter was incredibly blaze. I’m sick at the moment so I’m on benefits. They have put a lot of people in peril.”

Another resident, Sandra, who didn’t want to give her full name, told the Gazette: “I have been made extremely vulnerable by this because I am elderly and I can’t get around well without a crutch. It’s obvious why I don’t want people to know my address.

“I know that only 11 people viewed the document, but it only takes one or two bad people for this to be devastating. Lovely Christmas present from Hackney Homes.”

A spokesman from the Information Commissioners’ Office confirmed that it is currently making enquiries into the incident.

Hackney Homes chief executive Charlotte Graves said: “Hackney Homes and the Council takes data protection very seriously and we’re very sorry that this has happened.

“As soon as we were made aware, we ensured the information was removed and wrote to those residents whose details were included. We have also taken immediate action to ensure it does not happen again.”

A spokesman for the council added that the data “was accessible to those with detailed IT knowledge who could potentially manipulate the spreadsheet to reveal the information” and not a “casual viewer of the document”.

In the light of the incident, the council have warned residents to be vigilant of telephone scammers and have said they have taken necessary steps to ensure it will not happen again