The passwords and other details of 16 million email users in Germany have been stolen- the equivalent of almost a fifth of the German population being at risk.
More than half of the hacked accounts ended in ‘.de,’ the Internet country code for Germany.
Researchers and prosecutors found the hacked accounts while conducting research on a botnet, a network of computers infected with malware.
Germany’s Federal Office for Information Security (BSI) has created a website to help people find out whether or not their e-mail was among those hacked.
The site temporarily crashed on Tuesday due to heavy traffic. Users who submit their email address to the website will be sent an message if their account has been compromised.
“If that happens, then your computer is most likely infected with malware,” Tim Griese, with the Federal Office for Information Security, told the news agency DPA.
Authorities have not released information on who stole the e-mail accounts.
The Federal Office for Security said criminals had infected computers with software which allowed them to gather email addresses and account passwords.
The agency has not commented on what progress it has made in tracking down the hackers.