Be honest — how often do you use the same username and password on different websites or applications? According to InformationWeek, more than half of us do it.

Security experts warn that the practice leaves you vulnerable — if one site is hacked, your accounts on all sites and apps are compromised.

According to Dropbox, that’s exactly what happened in mid-October when someone posted 400 user names and passwords on Pastebin. Under the header, Dropbox.com Hacked, First Teaser, the person posting claimed to have nearly 7 million Dropbox name and password combinations and asked for bitcoin donations to prompt the release of more.

Dropbox was quick to fire back that no breach had happened on its servers. Instead, according to a Dropbox blog post, “Your stuff is safe. The usernames and passwords…were stolen from unrelated services, not Dropbox. Attackers then used these stolen credentials to try to log in to sites across the internet, including Dropbox. We have measures in place to detect suspicious login activity and we automatically reset passwords when it happens.”

In a previous blog post, Dropbox urged users to adopt two step authentication, “The idea behind two-step verification is to combine ‘something you know’ (like your password) with ‘something you have’ (like your phone) to add an extra layer of security. Once you’ve enabled this feature, Dropbox will either text you a six-digit security code to enter after your password or you can get the code from an authenticator app like Google Authenticator, which is useful if you can’t get a cell signal. Having two steps rather than just one creates a stronger barrier against attackers.”

The takeaway: use different usernames and passwords on all websites and applications.