Generally, since it does not offer any advertising or ads of its own, Pirate Bay is not illegal. It is essentially a forum for peer-to-peer sharing. Therefore, you can use it without doubt if you are in a country where the web hasn't been closed. And even if it has been blocked in your country, via the numerous pirate proxy sites open, you can still access it. There are mirror pages that have separate domain names and IP addresses, providing the same material that is accessible on the original platform. It is not feasible, however, to say authoritatively that any mirror site is safe. There are some that sell adware and other kinds of malware, while most of them are free.