HARTFORD, Conn. (AP) — Electric, natural gas and major water companies and regional distribution systems in Connecticut have been penetrated by hackers and other cyber attackers, but defenses have prevented interruption, state utility regulators said Monday in their first report on cyber security.

Security challenges are constantly evolving and “becoming more sophisticated and nefarious” and the ability of utilities to detect and stop penetration must constantly improve, the Public Utilities Regulatory Authority said in its report to Gov. Dannel P. Malloy.