Three families of victims killed in a 2015 terrorist attack in San Bernardino, California have sued Twitter, Google, and Facebook [npr.org], alleging that the tech giants knowingly supported ISIS by allowing it to build an online presence and recruit new members for attacks:
Similar lawsuits against social-networking companies have been dismissed by U.S. courts because of a law which immunizes online providers from liability over user postings.
Court records show that in previous cases, Google, Facebook and Twitter have said, while they are sympathetic to victims, they are not liable for what happened.