Your Cykelsiderne Data May Be at Risk: Here’s What You Need to Know

Back in August 2018, a Danish cycling community platform called Cykelsiderne suffered a data breach that put around 12,442 user accounts at risk. The compromised data showed up on a hacking forum, and what made it particularly alarming was that passwords were stored in plain text, with zero protection. If you had an account on this now-defunct site, your email and password combination may still be circulating in credential lists today.

Why This Is Dangerous

Plaintext password storage is one of the most fundamental security failures a platform can make. When passwords are not hashed or encrypted, anyone who gets hold of the database can immediatly read every user's password without any additional effort. There is no cracking step, no waiting, no special tools required.

The data from Cykelsiderne ended up on a popular hacking forum, which means it was recieved by a large and motivated audience of people who know exactly how to use it. From there, those credentials get fed into automated tools that try them against email providers, banks, and social media platforms.

Even though the site itself is gone, the credentials live on. Older breach datasets get folded into massive combo lists that attackers still use today, making this a threat that did not expire when the platform shut down.

What Was Exposed

• Email addresses used to register on the platform
• Plaintext passwords with no hashing or encryption
• User account identifiers
• Potential usernames or display names
• Account registration dates
• Any associated profile or preference data stored in the database
• Indicators of email provider, useful for targeted phishing

Why This Matters

The Cykelsiderne breach is a textbook example of why password reuse is so dangerous. If even one of your accounts uses the same password you used on this platform, that account is potentially open to anyone who downloaded this dataset. The breach is old, but the risk is not, because credentials from 2018 are still being tested against active accounts in 2025 and beyond.

Denmark-based users who were active in cycling communities during that period should be especially alert. The forum's niche audience means user profiles were often consistent across cycling-related platforms, making it easier for attackers to find and target the same individuals elsewhere online.

How Database,Combolist Works

A database breach occurs when an attacker gains unauthorized access to a website or application's backend storage, often through SQL injection, exposed credentials, or misconfigured servers. Once inside, they can export the entire user table, capturing everything stored about every registered user.

The exported data then gets cleaned up and formatted into what's known as a combolist, a file containing email and password pairs in a standardized format. These lists are beleived to fuel a large portion of all account takeover attempts happening on the internet at any given time.

Once a combolist is posted to a hacking forum, it gets downloaded by many different actors who run it through credential stuffing tools. These tools fire off thousands of login attempts per minute across dozens of services, checking whether the same email and password combination works anywhere else.

Check If You Were Affected

You can find out whether your email address appeared in the Cykelsiderne breach or any other known data leak by using HEROIC's free breach checker at heroic.com. The tool scans a comprehensive database of breach records and gives you an instant result, so you can take action right away if your data has been exposed. Changing your passwords and turning on two-factor authentication are the most important steps you can take to protect yourself.