The US Department of Homeland Security (DHS) on Monday said it was looking into an apparent cyberattack that affected tens of thousands of American travelers.
The DHS, in a statement on its website, said the incident was reported to US officials in March and that “there has been no impact to our systems”.
The attack affected US citizens, some with US passports, the DHS said.
The statement added that US citizens “should not take any actions that would place them at risk of any threat, and should be alert to the fact that they may be subject to such a threat”.
It said travellers should review the travel advisories for their country and that those travelling abroad should take steps to protect themselves.
The US has faced an unprecedented wave of cyberattacks since the election of President Donald Trump in November.