The hollow wont spread accross jungle biomes and crimson as stated on the wiki.
Despite its friendly looks, the Hallow is only slightly less dangerous
than the Corruption or Crimson. It spreads almost completely in the
same way as the Corruption except that it cannot spread through the
If you do not wish to have your world turned into just Hallow and Corruption/Crimson or even if you want to completely purify your world, containment is key. A simple and also the best way of containment is making straight tunnels from the surface down to the Underworld (commonly called Hellevators) that are three block wide. An easier way would be to place block from the opposite biome of what your are containing around it(Example: Surrounding the Corruption with Hallowed) to stop the spread. The obvious drawback to this plan is that you will have to deal with the biome you're using to contain the other biome with.
Protecting the Jungle
Since the Corruption/Crimson cannot spread past Hallow, and the Hallow cannot spread past the Jungle, you can line the edges of your Jungle with Hallowed blocks to prevent damage to it. This will however only prevent surface spreading.
Your question is sort of answered here : How does corruption spread?