After not updating the Wii U for over a year and a half Nintendo released the 5.5.2 update, which patched some vulnerabilities in the web browser which had been used by the community to launch Homebrew on the Wii U.
However its rumoured the Crunchyroll App can also be exploited for Homebrew purposes. With that in mind if you have updated to 5.5.2 we'd recommend download the Crunchyroll App, just in case. Better to be safe than sorry right?!