ahh i see, gonna cleanse that area, thanksThat's easy -- it looks like you've got corruption under the house. Take a look at the minimap, you've got purple coming out of the shadowed area, and a little corruption gives you "This housing is not valid" if it's within about a screen of the house in question, instead of "This housing is corrupted" when it's basically sitting out in the corruption.
1 Question, how the corruption can spread without any source?, i digged into that area and theres only normal terrain and hollow, its like the corruption came out of nowhereThat's easy -- it looks like you've got corruption under the house. Take a look at the minimap, you've got purple coming out of the shadowed area, and a little corruption gives you "This housing is not valid" if it's within about a screen of the house in question, instead of "This housing is corrupted" when it's basically sitting out in the corruption.
When you break altars, it randomly picks a square to be hallowed, and one to be corrupted, but considering all I know of your world is what you have shown, there's every chance it could have been a patch of ebonstone or ebonsand in the unexplored area.1 Question, how the corruption can spread without any source?, i digged into that area and theres only normal terrain and hollow, its like the corruption came out of nowhere