In Ann M. v. Pacific Plaza Shopping Center (1993) 6 Cal.4th 666, a shopping mall provided no security guards, even though its tenants complained that transients loitered in the mall's common areas. (Ann M., supra, 6 Cal.4th at pp. 670-673.) After a tenant's employee was raped inside the tenant's store, she initiated a negligence action against the mall. (Id. at pp. 670-671.) When the mall sought summary judgment on the ground that it lacked a duty to protect the employee, she maintained that violent crimes had occurred within the mall, but offered no evidence that the mall had notice of those incidents. (See id. at pp. 679-680.) In holding that the mall had no duty to hire security guards, the Supreme Court explained that the scope of a landlord's duty "is determined in part by balancing the foreseeability of the harm against the burden of the duty to be imposed." (Ann M., supra, 6 Cal.4th at p. 678, quoting Isaacs v. Huntington Memorial Hospital (1985) 38 Cal.3d 112, 125.) Because the social costs of requiring landlords to hire private guards are "not insignificant, . . . a high degree of foreseeability is required in order to find that the scope of a landlord's duty of care includes the hiring of security guards." (Ann M., supra, at p. 679.) In contrast, when "'"harm can be prevented by simple means, a lesser degree of foreseeability may be required."'" (Ibid.) Under these principles, the foreseeability of crimes warranting the hiring of security guards or similarly costly measures can "rarely, if ever," be proven, absent notice to the landlord of prior similar incidents. (Ibid.) In a footnote, the court clarified the qualification to the "prior similar incident" standard, stating: "It is possible that some other circumstances such as immediate proximity to a substantially similar business establishment that has experienced violent crime on its premises could provide the requisite degree of foreseeability." (Ibid., fn. 7.)