SAN FRANCISCO — The Securities and Exchange Commission in new guidance Wednesday urged public companies to guard against insider trading before cybersecurity breaches are disclosed and to ensure there are clear internal procedures in place to determine when a hack might be “material” to investors.

The 24-page guidance, formally adopted Tuesday, is the first to be issued on cybersecurity by the SEC commissioners. The SEC staff issued a shorter guidance document in 2011 focusing primarily on how companies should disclose cyber risks and incidents, and how threats might affect their financials. The new guidance underscores how critical cyber infrastructure has become to modern business, comparing it to “the importance of electricity and other forms of power in the past century.”