Is an insurer obligated to defend an action against its insured?

"[A]s long as the [underlying] complaint contains language creating the potential of liability under an insurance policy, the insurer must defend an action against its insured." CNA Casualty v. Seaboard Sur. Co., 176 Cal.App.3d 598, 606, 222 Cal.Rptr. 276, 279 (1986). Moreover, "[t]he insurer's obligation to defend is not dependent on the facts contained in the complaint alone; the insurer must furnish a defense when it learns of facts from any source that create the potential of liability under its policy." Id. (emphasis in original).