Rabbi Matisyahu Salomon, a longtime spiritual counselor at America’s largest yeshiva who spearheaded a crusade to warn observant Jews of the risks posed by the internet, died on Jan. 2 in Lakewood, N.J. He was 86.

The death was confirmed by Rabbi Avi Shafran, public affairs director of Agudath Israel of America, the umbrella organization for numerous Hasidic and other ultra-Orthodox groups. He said Rabbi Salomon had been ill for many years.