SPRINGFIELD, Ill. — With the Illinois primary just days away, state election officials are beefing up cyber defenses and scanning for possible intrusions into voting systems and voter registration rolls.

They have good reason to be on guard: Two years ago, Illinois was the lone state known to have its state election system breached in a hacking effort that ultimately targeted 21 states.

Hackers believe to be connected to Russia penetrated the state’s voter rolls, viewing data on some 76,000 Illinois voters, although there is no indication any information was changed.

Since then, Illinois election officials have added firewalls, installed software designed to prevent intrusions and shifted staffing to focus on the threats. The state has been receiving regular cyber scans from the federal government to identify potential weak spots and has asked the U.S. Department of Homeland Security to conduct a comprehensive risk assessment. That assessment is scheduled but will not happen before Tuesday’s primary.

“It’s not something where you ever feel completely safe,” Matt Dietrich, spokesman for the Illinois State Board of Elections. “It’s something where you feel like you’re doing your best to protect against what could happen in a cyberattack.”

Federal intelligence agencies determined that the attempted hacking of state elections systems in 2016 primarily targeted voter registration systems, not actual voting machines or vote tallying.

Cybersecurity experts say it’s crucial for states to shore up vulnerabilities.