According to media reports, hackers have threatened to publish data from the Israeli LGBTQ dating site Atraf - if the operators don't pay the equivalent of around 870,000 euros.
"We are dealing with an Iranian cyber terrorist incident," Israeli television quoted from a statement by the site operator on Sunday.
They are working on offering the service again, but only with comprehensive security - including resetting the passwords of all users.
LGTBQ is the English abbreviation for lesbian, gay, bisexual, transsexual and queer.
Atraf did not initially respond to a request from the German Press Agency.
According to Israeli media reports, the hacker group Black Shadow is alleged to consist of Iranian criminals.
In addition to Atraf, other Israeli companies were also affected by the hacking attack, such as two public transport companies, according to media reports.
The hackers have already published sensitive data.
For example, homosexual users of Atraf worried that they would be unintentionally outed.
Several people in the network also reported about their HIV infection.
On a Telegram channel called “Black Shadow” it was said that the Atraf database contained the data of around one million users.
If the operators paid a million dollars within 48 hours, the data would not be published.
On Sunday, Iran blamed its political arch enemies Israel and the USA for a cyber attack on the nationwide gas station network.
"The investigations are still ongoing, but we believe that the Americans and the Israelis are definitely behind it," said the Iranian head of the cyber security department, according to media reports.
The cyber attack on the payment system of the petrol stations caused long lines and chaos in the capital Tehran and other cities on Tuesday.