Data breaches → KnownCircle
Was your data in the KnownCircle breach?
2016 · knowncircle.com · ~1,957,600 accounts exposedCritical severity · 10/10
KnownCircle (knowncircle.com) suffered a data breach in 2016 that exposed around 1,957,600 accounts. If you had an account, some of your personal data may be circulating in leaked databases. The fastest way to know is to check your own email — free, in about 30 seconds, no password required.
What happened
In approximately April 2016, the "marketing automation for agents and professional service providers" company KnownCircle had a large volume of data obtained by an external party. The data belonging to the now defunct service appeared in JSON format and contained gigabytes of data related to the real estate and insurance sectors. The personal data in the breach appears to have primarily been used for marketing purposes, including logs of emails sent and tracking of gift cards. A small number of passwords for KnownCircle staff were also present and were stored as bcrypt hashes.
Breach details sourced from Have I Been Pwned, the industry-standard breach database. Risk analysis by Nullivo.
What was exposed, and why it matters
Not all breaches carry the same risk — what matters is which fields leaked. Here is what the KnownCircle breach exposed and what each item actually enables:
Attackers replay leaked passwords across other sites (“credential stuffing”). Because most people reuse passwords, one leak often unlocks email, shopping and banking accounts elsewhere.
Personal correspondence can be used for blackmail or social engineering, and often contains other sensitive details you have forgotten sharing.
Home addresses feed people-search and data-broker sites, which republish them publicly. They also make phishing far more convincing and, in the worst cases, enable real-world harassment.
Enables SIM-swap attacks (hijacking your number to intercept SMS codes), smishing, and voice scams that appear to come from your bank.
Links this leak to your other accounts — a reused username lets anyone build a profile of you across platforms.
Puts you on spam and phishing lists, and confirms to attackers that you hold an account with this service — which makes impersonation emails more believable.
Also listed in this breach: Email addresses, Email messages, Genders, Names, Passwords, Phone numbers, Physical addresses.
What to do if you were affected
These steps are ordered for this specific breach — the most urgent action given what leaked comes first.
- Passwords: Change this password everywhere you have reused it, starting with your email account — whoever controls your email can reset everything else.
- Private messages: Consider what was discussed on this service and whether anything needs changing (shared passwords, personal disclosures).
- Home addresses: Get your address removed from data brokers — they re-list roughly every four months, so this needs repeating.
- Phone numbers: Move two-factor authentication off SMS to an authenticator app or passkey, and add a port-out PIN with your mobile provider.
- Names and usernames: Search your usual username to see what else it exposes, and use distinct handles for sensitive accounts.
- Check whether your own email appears in this breach — run a free scan to confirm before you spend time on the steps above.
This breach put your details on data-broker sites
Because KnownCircle exposed home addresses, this is one of the breaches that feeds people-search and data-broker sites. Those sites scrape leaked databases, combine them with public records, and republish the result as a searchable profile — which is how a single breach turns into a permanent public listing. Removal works, but brokers typically re-list within about four months, so it has to be repeated.
See our broker-by-broker removal guides →
How urgent is this now?
This breach is over 10 years old. Old credentials still cause harm — leaked passwords from a decade ago are still tried against new accounts every day.
Passwords are the reason breach age matters less than people expect. Leaked credentials are compiled into wordlists that get tried against new services for years afterwards, so a password exposed here is unsafe to use anywhere, ever again.
Remember: a breach can't be "un-leaked" — once a database is out, it exists in countless copies. The goal is to make the leaked data useless: change what can be changed, lock down what can't, and remove what has been republished.
Frequently asked questions
What data was exposed in the KnownCircle breach?
The KnownCircle breach exposed passwords, private messages, home addresses, phone numbers, names and usernames, email addresses. Attackers replay leaked passwords across other sites (“credential stuffing”). Because most people reuse passwords, one leak often unlocks email, shopping and banking accounts elsewhere.
How many people were affected by the KnownCircle breach?
Around 1,957,600 accounts were exposed, making it a large breach.
What should I do if I had a KnownCircle account?
Change this password everywhere you have reused it, starting with your email account — whoever controls your email can reset everything else. You can check whether your own email appears in this breach with a free Nullivo scan — no password required.
Breaches that exposed similar data
If the KnownCircle breach affected you, these breaches exposed comparable information — worth checking too, since leaked datasets are routinely combined.
- Was your data in the Ster-Kinekor breach? (2017, ~1,619,544 accounts)
- Was your data in the Fashion Nexus breach? (2018, ~1,279,263 accounts)
- Was your data in the NapsGear breach? (2015, ~287,071 accounts)
- Was your data in the eThekwini Municipality breach? (2016, ~81,830 accounts)
- Was your data in the ClearVoice Surveys breach? (2015, ~15,074,786 accounts)
- Was your data in the VNG breach? (2015, ~24,853,850 accounts)