Several German airports had their websites disrupted on Thursday, with experts investigating a possible online attack.
The problems come a day after a major IT failure at Germany's national carrier Lufthansa left thousands of passengers stranded at Frankfurt airport.
"Once again, airports fell victim to large-scale DDoS attacks," Ralph Beisel. chief executive of the ADV airport association, said in a statement.
"According to the information we have so far, other systems are not affected," she said, adding it was not clear whether the situation will spread to other locations.
What we know so far
Among the airports affected were Düsseldorf, Nüremberg, Erfurt-Weimar and Dortmund. The websites were either not reachable or flagged up failure messages.
The websites of Germany's biggest airports, in Frankfurt, Munich and Berlin, were operating normally.
"We are still troubleshooting," a spokeswoman for Dortmund Airport said, adding it was unlikely that the failure was due to a regular overload.
"There is reason to suspect it could be a hacker attack," she said.
Nüremberg Airport in northern Bavaria said its site had been receiving so many requests that it collapsed. German news magazine Spiegel's website reported that the problems could have been caused by a DDos attack, in which hackers direct heavy internet traffic at targeted servers in a relatively unsophisticated effort to take them offline.
There were no reported effects on air traffic.
There was travel chaos at Frankfurt Airport — one of Europe's biggest airports — on Wednesday after cable damage at a construction site caused a computer system failure, with more than 200 flights canceled.
The websites of German airports were among multiple targets believed to have been brought down last month by the pro-Russian hacking group Killnet.
rc/fb (Reuters, dpa)
While you're here: Every Tuesday, DW editors round up what is happening in German politics and society. You can sign up here for the weekly email newsletter Berlin Briefing.