The websites of at least three German airports were disrupted on Thursday, Reuters reports.

Among the airports affected were Dusseldorf, Nuremberg, and Dortmund, but sites for Germany’s biggest airports, in Frankfurt, Munich, and Berlin, were operating normally.

Buy Me A Coffee

Focus Online, which initially reported the outage, gave no reason for the problem.

Spiegel Online reported that the problems could have been caused by a DDos attack, where high volumes of internet traffic are directed to targeted servers in a relatively unsophisticated bid by so-called “hacktivists” to knock them offline.

Meta, Match Group, Coinbase, Others Team Up to Prevent, Disrupt Financial Scams