Hundreds of IP addresses were listed in an annexe to the FBI's joint analysis report attributing malicious cyber activity across the world to Russian hackers.
Of those, three IP addresses were listed as being from Swaziland.
However, analyzing the list, Danish IT news site Version2 found that they were actually Swiss IPs, it said on Monday, something that is easily confirmed via an online IP address checker.
The IPs in question are thought to have been hacked by the group Fancy Bears, suspected by the US of having links to the Russian government.
In total Version2 noticed 18 anomalies in the FBI's list, including some German IPs listed as Danish, perhaps due to the similarity between the .de and .dk country codes, it said.
Speaking to the site, a Danish expert said these were probably just typing errors and didn't reflect on the thoroughness of the FBI investigation.
It's not the first time Switzerland has been confused with another country.
In 2013 the Swedish consulate in China launched a competition to help the Chinese tell Switzerland apart from Sweden, since the two country names are very similar in their language.