A security update from McAfee antivirus software caused some computers at Kansas University Hospital to go down from about 11 a.m. until about 2:30 p.m. Wednesday.

A hospital spokesman said systems overseeing patient care were not affected, though many tasks, such as looking up medical records, took longer while the problem was being resolved.

In a blog on the company’s website, McAfee officials said that the faulty update affected Windows computers, and estimated that it affected less than one-half of 1 percent of its global consumer base and enterprise accounts.