The head of the FBI said Wednesday that the government will bring more legal cases over encryption issues in the near future, according to Reuters.

Speaking with reporters at FBI headquarters in Washington, FBI Director James Comey specifically said that end-to-end encryption on WhatsApp is affecting the agency’s work in "huge ways." However, he noted the FBI has no plans to sue Facebook, the app’s parent company.

He also said that since October 2015, the FBI has examined "about 4,000 digital devices" and was unable to unlock "approximately 500."

The FBI paid gray hat hackers at least $1.3 million for a way to get into the seized iPhone used by Syed Rizwan Farook, the now-dead terrorist involved in the December 2015 attack in San Bernardino, California. At the last minute, the Department of Justice canceled a highly anticipated court hearing over the issue in March 2016.

However, Comey said that the hackers' identities are so closely held inside the government that even he doesn’t know who they are, according to Reuters.