Facebook beat estimates for daily active users on Wednesday, but the company's operating margins dropped for the world’s largest social network after it ramped up spending to improve content and security across its platforms.

The world’s biggest social-media company reported record fourth-quarter revenue of $21.1 billion, boosted by ads on Instagram and in video. The 25% increase from the period a year earlier was the slowest-ever quarterly sales growth for the company. Facebook said it had 2.89 billion users of its products around the world, but the growth on the main social network -- the primary source of advertising sales -- has started to slow.

Total costs and expenses surged 34% to $12.22 billion in the fourth quarter, dragging down operating margins to 42% from 46% a year earlier.

Facebook has faced scrutiny over the past three years from regulators and users worldwide over its privacy practices and data breaches. It is also facing the heat over how its services have been allegedly used to spread misinformation.

The company makes money mainly from ads, and its profitability depends on its Facebook, WhatsApp, Instagram and Messenger properties. The company is trying to find future revenue streams with not much success so far -- artificial intelligence, virtual reality and shopping.

Still, Facebook and Google dominated digital ad spending with an estimated 61% of the market in 2019, a slight increase from a year earlier, even as Amazon.com Inc. gains sales, researcher EMarketer said in November.

Facebook’s main social network had 2.5 billion monthly active users as of Dec. 31, slightly topping analysts’ estimate of 2.49 billion.

Quarter highlights

• Daily active users rose to 1.66 billion.
• Ad sales jumped 25% to $20.74 billion in the quarter.
• Net income rose to $7.35 billion, or $2.56 per share, in the three months ended Dec. 31, from $6.88 billion, or $2.38 per share, a year earlier.
• Total revenue rose 24.6% to $21.08 billion, beating estimate of $20.89 billion.