SAN FRANCISCO — The vast majority of videos removed from YouTube toward the end of last year for violating the site’s content guidelines had first been detected by machines instead of humans, the Google-owned company said on Monday.

YouTube said it took down 8.28 million videos during the fourth quarter of 2017, and about 80 percent of those videos had initially been flagged by artificially intelligent computer systems.

The new data highlighted the significant role machines — not just users, government agencies and other organizations — are taking in policing the service as it faces increased scrutiny over the spread of conspiracy videos, fake news and violent content from extremist organizations.

Those videos are sometimes promoted by YouTube’s recommendation system and unknowingly financed by advertisers, whose ads are placed next to them through an automated system.