NEW YORK (BLOOMBERG) - Facebook chief executive officer Mark Zuckerberg, criticised for months by lawmakers, privacy advocates and some investors, said he was "proud of the progress we've made," fighting misinformation and protecting users' personal data during one of the company's most tumultuous years.

"To be clear, addressing these issues is more than a one-year challenge," Zuckerberg said in a Facebook post.

"For some of these issues, like election interference or harmful speech, the problems can never fully be solved."

This year was one of constant apologies for the social network, after multiple instances of broken trust with its users.

Zuckerberg testified for the first time in front of Congress in April, explaining why Facebook allowed users' data to fall into the hands of unauthorised third parties.

In his reflection on Friday (Dec 28), he made the case that Facebook is now a changed company, and will be more proactive about problems.

"We've fundamentally altered our DNA to focus more on preventing harm in all our services," he wrote.

The blows to Facebook's reputation also have hurt the stock, which declined 24 per cent this year through Thursday's close, while the S&P 500 dropped 6.9 per cent. The shares fell about 1 per cent to US$133.28 at 1.32pm on Friday in New York.

In Zuckerberg's list of things Facebook accomplished in 2018, some remain undone, or already widely critiqued.

For example, he writes that Facebook automatically takes down 99 per cent of terrorist content before anyone reports it, without saying that the statistic only refers to content from Islamic State in Iraq and Syria and Al-Qaeda.

He also points to a "clear history" tool the company started building.

Facebook announced the tool in May, but it will still be many months before it rolls out to users.