Election interference and harmful speech are issues that "can never fully be solved" by Facebook, according to the social media giant's embattled boss.
In an end-of-year post on Mark Zuckerberg's own Facebook page, the chief executive claimed the company had "fundamentally altered our DNA to focus more on preventing harm in all our services" during the year.
He noted that his biggest personal challenge for the year has been to address some of the issues that have caused the company to draw intense criticism in 2018.
Earlier this year, Facebook was embroiled in a scandal over the harvesting of the personal data of 87m users by Cambridge Analytica, a political consulting firm, which used it for political reasons. The firm went on to work for the campaign of Donald Trump, the US president.
It has also struggled with hate speech on its platform, which has contributed to violent attacks against a minority Muslim population in Myanmar.
The remarks from Mr Zuckerberg come amid a US government shutdown, which threatens to delay a probe by the Federal Trade Commission into the company's handling of user data.
Facebook claims it now now has more than 30,000 people working on safety and has invested "billions of dollars in security" per year.
However, the company's boss suggested that the measures would not be enough to help Facebook "catch every bad actor or piece of bad content".
"They're challenges against sophisticated adversaries and human nature where we must constantly work to stay ahead," Mr Zuckerberg wrote in his post.
The chief executive stressed that Facebook is "a very different company today" than it was in 2016, when Cambridge Analytica started to work for the presidential campaign of Donald Trump and pro-Brexit group Leave.EU.
It has shifted "a large portion" of the company to work on preventing harm.
Facebook's measures for preventing election interference and the spread of harmful speech include systems for identifying coordinated information campaigns and AI systems designed to automatically identify content related to terrorism, Mr Zuckerberg added.