The method allegedly used by China to view the networks of US technology companies was not complex enough, according to Jamil Jaffer, a senior senior adviser to the Senate Foreign Relations Committee.
"It was a strange effort by the Chinese [which] we know they're pretty clever, "he said, speculating that the hacks actually happened.
It is normal for another country to join or gain access to another government's system, said Jaffer.
However, he added that over the years the US has become more and more aggressive with China, which has led China to limit its cyber intrusions, but "they are still making very concentrated efforts."
China is also intensively examining President Donald Trump, who has used Chinese allegations of intellectual property theft as the core argument for tough trade restrictions against Beijing.
CNBC reported Monday that the Pentagon has canceled Defense Secretary James Mattis' visit this month amid mounting tensions with China.