An online attack disrupted call operations for Hillary Clinton’s presidential campaign ahead of Tuesday’s election.

NextGen Climate, an advocacy group that supports Mrs. Clinton, experienced problems with its phone-dialing software Monday following an online attack, according to Suzanne Henkels, a NextGen Climate spokeswoman.

The attack hit TCN Inc., a St. George, Utah, company that provides phone-dialing services accessible via the internet to NextGen Climate and other groups.

A TCN spokeswoman said the problems occurred in waves, lasting about an hour, starting at 2:35 p.m. ET Monday, slowing TCN’s services and leaving them unavailable for “a few brief periods.”

The hiccups emerged after an anonymous poster on the 4chan message board claimed that he planned to use a version of the Mirai botnet to attack TCN in hopes of harming Mrs. Clinton’s campaign. The Mirai botnet was behind the Oct. 21 attack that left portions of the internet inaccessible. Mirai software that can be used to take over a variety of devices—routers, internet- connected cameras and DVRs, for example—and use them to attack other computers by flooding them with useless information.