SAN FRANCISCO — People talk about online security as a cat-and-mouse game of good guys and bad guys. It’s true for good old-fashioned crime, too.

Technology, particularly rapid analysis and sharing of data, is helping the police be more efficient and predict possible crimes. Some would argue that it has even contributed to an overall drop in crime in recent years.

But this type of technology also raises issues of civil liberties, as digital information provided by social media or the sensors of the internet of things is combined with criminal data by companies that sell this information to law enforcement agencies.

The American Civil Liberties Union, citing reports that the Chicago Police Department used a computer analysis to create a “heat list” that unfairly associated innocent people with criminal behavior, has warned about the dangers of the police using big data. Even companies that make money doing this sort of work warn that it comes with civil rights risks.