About 18 percent of computers worldwide encountered a virus or malware last year, down from 19 percent the previous year, Microsoft said in a report outlining the state of cybersecurity threats. But the rate of infections was far lower, Microsoft says. Just 0.9 percent of computers using Microsoft’s malware removal tool last year had been infected by malicious software, little changed from 2014. People were most likely to encounter malware in North Africa, the Middle East and Southeast Asia.