Around 16 million German email users have had their account details compromised by hackers, according to the country's Federal Office for Security (BSI).
It said cybercriminals had infected computers with software that collected email addresses and passwords. The agency has set up a website for people to check if their accounts have been compromised, although this has crashed a few times under the weight of demand by worried users.
"In the analysis of botnets by research institutions and law enforcement agencies around 16 million were compromised user accounts," said the BSI in a statement (translated from German). "The email addresses have been handed over to the BSI so affected users can be informed and take necessary protective measures."
The agency warned affected users could be at risk of identity theft as a result of the hack. It said those affected should check PCs for malware and change passwords for email accounts, social networking sites and online stores. It also warned affected users to do this sooner rather than later.
The BSI has not said when it analysed the botnet, when the attack took place or who might be behind the attack.
The incident is the latest in a long line of security breaches. In South Korea up to 100 million credit card details and accounts were compromised, and sold onto marketing companies, according to a Reuters report.
The theft is thought to have been undertaken by a contractor working for the Korea Credit Bureau who simply uploaded the information onto a flash drive. The alleged theft took place in February, June and December last year, according to the country's regulator the Financial Supervisory Service.
