The tech king also admitted special counsel Robert Mueller had interviewed his staff
"This is an arms race. They're going to keep getting better," Zuckerberg said of Russia, when interrogated about user privacy and electioneering on his social media platform.
He was being questioned by American politicians in the wake of the Cambridge Analytica scandal, which Facebook believes has affected 87 million users.
US senators heard how Zuckerberg's company is in a perpetual battle with the Russian state. The executive also revealed that Robert Mueller, the special counsel investigating alleged Russian meddling in the 2016 US election, had interviewed Facebook employees - some of whom had been subpoenaed.
Mr Zuckerberg said he has not been among those interviewed by Mr Mueller's office.
"Our work with the special counsel is confidential and I want to make sure that in an open session I'm not revealing something that's confidential," he said.
"There are people in Russia whose job it is to try to exploit our systems and other internet systems and other systems as well. We need to invest in getting better at this too."
When pressed on regulation, the 33-year-old billionaire said he would accept it if it was the "right regulation."
He was appearing in front of a joint session of several US senate committees.
After the first break in proceedings Facebook's share prices had risen by 5 per cent, netting the Zuck a cool $3 billion personally.
