Cybersecurity surrounding the U.S. electoral system has been a focus this election cycle, not least since Russian hackers have actually found their way into the Democratic Party’s network and state voter rolls, and WikiLeaks has apparently obtained and published emails allegedly belonging to Hillary Clinton campaign chair John Podesta.

Republican nominee Donald Trump has repeatedly claimed — without any evidence whatsoever — that the election might be “rigged” against him. As he cast uncertainty over whether he would accept the Nov. 8 vote’s result in Wednesday’s final televised presidential debate, U.S. intelligence and law-enforcement sources are warning that Russian hackers could undermine the American public’s trust in the electoral process by posting fake evidence of voter fraud online.

Read More: Donald Trump’s ‘Rigged’ Election Talk Amounts to Voter Suppression

Reuters reports Thursday that these officials, speaking on conditions of anonymity, said that hackers affiliated to Russian intelligence agencies could produce fake documents purporting to show signs of electoral rigging and disseminate them online, in the hopes of creating public perception of widespread foul play in the general election.

They said that, while there was no evidence of such a scheme in the works, state and local authorities were warned to be ready and take precautions against hacking attempts.

These officials also stressed that the large and dispersed electoral operation — conducted locally by states and local authorities instead of a centralized U.S. federal government operation — means that hackers would be unable to actually alter the election’s outcome.

[Reuters]

Get our Politics Newsletter. The headlines out of Washington never seem to slow. Subscribe to The D.C. Brief to make sense of what matters most. Please enter a valid email address. Sign Up Now Check the box if you do not wish to receive promotional offers via email from TIME. You can unsubscribe at any time. By signing up you are agreeing to our Terms of Use and Privacy Policy . This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply. Thank you! For your security, we've sent a confirmation email to the address you entered. Click the link to confirm your subscription and begin receiving our newsletters. If you don't get the confirmation within 10 minutes, please check your spam folder.

Contact us at letters@time.com.