MADISON, Wis. (AP) — Wisconsin election officials are refusing to name a handful of local clerks that testing showed may be vulnerable to cyberattacks.

The state Elections Commission asked all 2,700 local clerks to log into the state election system this summer. Commission staff in August said they detected five clerks using outdated software.

The Associated Press filed a records request seeking the clerks’ names. The commission said in a letter Thursday that releasing the names would invite hackers to disrupt election administration and chill discussions about vulnerabilities.

The letter said only four clerks were using outdated and unsupported systems, not five as staff originally thought. Commission spokesman Reid Magney said in a text Thursday that one clerk was using Windows XP, two were using Vista and another was using an outdated Macintosh system.

They’ve all since received upgrades.