The internet dating site appears to have been hit by the same cyber attack as LinkedIn, which reportedly saw around 6.5 million of its encrypted passwords posted on a Russian hacking forum.
It has since emerged that scores of eHarmony passwords were mixed in with the LinkedIn ones. The website has reset the accounts of users who were affected as a precautionary measure.
"After investigating reports of compromised passwords, we have found that a small fraction of our user base has been affected," read a statement from corporate communications manager Becky Teraoka.
"We are continuing to investigate but would like to provide the following actions we are taking to protect our members. As a precaution, we have reset affected members' passwords. Those members will receive an email with instructions on how to reset their passwords."
It has yet to be confirmed how the user data was leaked online.