The three men, aged 43, 42 and 39, were detained after a roadside check in Warsaw, Polish state news agency PAP reported on Monday.
They told police they were "travelling around Europe," had arrived in Poland a few hours earlier and were planning to head to Lithuania.
Police carried out a thorough search of the car, finding advanced equipment that could be used even for interference with strategic information systems, according to officials.
The search yielded what investigators described as a spy equipment detector and "advanced hacking equipment," in addition to aerials, laptops, a large amount of SIM cards, as well as routers, mobile hard disks and cameras, the PAP news agency reported.
The three Ukrainian nationals "were unable to specify" what they had intended to do with the confiscated items, officials said.
The suspects claimed to be "IT specialists" but "when asked more precise questions ... they pretended not to understand what was being said to them," police told reporters.
Prosecutors said they charged the men with "computer fraud and obtaining hardware and software designed to commit crimes, including an attempt to damage IT data of special significance to national defence."
The court sided with the prosecutors and ordered that the three men be detained for three months.
Poland’s security minister, Tomasz Siemoniak, last month urged Ukrainians living in the country not to be drawn into spying or sabotage on behalf of Russia, warning that Moscow uses financial incentives to recruit “disposable agents.”
He made the appeal after two Ukrainian nationals were arrested on suspicion of spying on Polish military infrastructure and supply routes used to deliver aid to Ukraine.
(pm/gs)
Source: PAP, IAR, twoje-miasto.pl