The website of Sweden's Transport Agency (Transportstyrelsen) was partially down on Thursday morning, according to the agency most likely as a result of a DDoS attack.
During a DDoS attack (Distributed Denial of Service), a website is bombarded with communication requests so that the servers become overloaded and the site crashes.
The website was back up again by 10 am, but a spokesperson told Swedish public broadcaster SVT that they were continuing to investigate in order to be able to confirm who or what caused the problems.
Public transport operators Västtrafik in western Sweden were also hit by two similar overload attacks on Thursday, briefly crashing its ticket booking app and online travel planner.
The incidents come a day after Sweden's Transport Administration (Trafikverket) was targeted in what was later confirmed as a DDoS attack, causing train delays across large parts of Sweden.
"It could be a prank or someone trying to investigate what kind of protection Trafikverket has," Patrik Gylesjö, deputy CEO of internet provider DGC told Computer Sweden.