More than a quarter of data breach incidents in 2016 took at least one month for companies to discover, and one in 10 had gone unnoticed for at least a year. That’s according to the latest report on data breaches from Verizon’s security research division, which analyzed 1,935 breach incidents reported by 65 organizations.

The share of breaches that took months or years to detect was higher in 2016 than it’s been since at least 2010, according to the report.

More than a quarter of incidents in 2016 had gone unnoticed for months or more, but there was also a big jump in the proportion of breaches discovered in minutes, hours, or days.

According to the report, however, almost two-thirds of the breaches that were discovered in days or less were associated with incidents that are easy to catch, like physical theft or administrative accidents. Breaches that took months or longer to detect, on the other hand, largely fell into categories like “cyber-espionage,” “point-of-sale intrusions,” and “privilege misuse.” It’s not clear from the data why there were big increases in the share of incidents discovered at both the long and the short end of the timescale.