Armed police officers were sent to the home of the founder of Mumsnet after a hacker made a hoax call as part of a wider attack on the parenting forum and its 7.7 million users.

Justine Roberts said the website, which has more than 14m visits a month, was forced offline during a cyber-attack claimed by an internet troll called @DadSecurity on Twitter who posted taunts such as “RIP Mumsnet” on the social network. She urged all Mumsnet users to change their passwords immediately amid fears the hacker or group of hackers have taken control of at least 11 accounts.

Metropolitan police officers were sent to Roberts’ home after the hacker called 999 claiming a gunman had been seen nearby, in what is known as a “swatting attack”. Another Mumsnet user was left “pretty shaken up” after police arrived at her house in the middle of the night after she interacted with @DadSecurity online, Roberts said. The Twitter account has now been suspended.

In an email to users, Roberts said: “To add to the ‘fun’, it seems @DadSecurity also resorted to swatting attacks. Swatting is a criminal practice in which someone makes an emergency call to the police claiming that a crime is taking place at the house of the intended victim, in order to get the police to send out an swat team to the address. An armed response team turned up at my house last week in the middle of the night, after reports of an armed man prowling around.

“A Mumsnet user who engaged with @DadSecurity on Twitter was warned to ‘prepare to be swatted by the best’ in a tweet that included a picture of a Swat team, after which police arrived at her house in the middle of the night following a report of gunshots. Needless to say, she and her young family were pretty shaken up. It’s worth saying that we believe these addresses were not gained directly from any Mumsnet hack as we don’t collect addresses. The police are investigating both instances.”

Swatting attacks have become common in the US, taking their name from the militarised Special Weapons and Tactics (Swat) units called to deal with armed incidents. The practice is common among gaming communities.

After a so-called distributed denial of service (DDoS) attack on 11 August, Mumsnet was restored on 12 August but it soon become clear the forum’s administrative functions had been hacked. Roberts said Mumsnet was confident that users’ passwords had not been accessed, but over the weekend a user reported that posts had been made falsely under her name.

It is believed the hacker accessed passwords through a form of phishing, in which a fake Mumsnet login page was created, allowing the cyber-attacker to see passwords in plain text when they were typed in. There is evidence of 11 user accounts being hacked.

“We take great care to protect the information you give us and not to ask for or store any more information than we need to run the site, but though we can’t know how many accounts have been affected, there have been enough breaches for us to ask all Mumsnet users to change their passwords,” Roberts said.

In April last year, Mumsnet warned that users’ data had been obtained by hackers exploiting the so-called Heartbleed bug, which gave access to information submitted via the login page, including usernames, emails and passwords.

There were reports on Wednesday evening that the website was intermittently down after another apparent denial-of-service attack.

