The Department of Homeland Security on Saturday urged state election officials to seek assistance in boosting cyber security ahead of November’s elections, after hackers tapped into voter registration systems in a small number of states. In a statement, Homeland Security Secretary Jeh Johnson said 21 states have sought the Department’s assistance to improve cyber security. Johnson said hackers have been scanning state computer systems, a possible prelude to actual cyber attacks. “These challenges aren’t just in the future — they are here today,” Johnson said. “We must remain vigilant and continue to address these challenges head on. Before November 8, I urge state and local election officials to seek our cybersecurity assistance.” At least four states have had voter registration systems hacked in recent weeks. Officials in Arizona and Illinois said their systems had been improperly accessed this summer, and ABC News reported Thursday that at least two other voter registration systems were compromised. But those voter registration systems are distinct from vote tabulation systems, which county, local and state election officials maintain independently of internet-based systems. That makes the tabulation system much more difficult to hack, experts say, without physical access to the tightly guarded voting machines themselves.