How can I challenge a granted Taiwanese patent?

The opposition system was abolished in 2004, and now the only way to a challenge a granted patent is through the invalidation procedure. Invalidation can be requested by anyone at any time. After the end of the patent term, however, only an interested party can request invalidation. Partial invalidation was introduced in the amended Patent Act which entered into force on 1 January 2013. Invalidation ex officio by TIPO was abolished in 2013.