It's hiding underneath foundations, in doors and window frames and other places. In some buildings, it's in plain sight.
It's mold, and it's rampant in houses flooded by Superstorm Sandy three months ago. It can cause coughing, wheezing and other respiratory problems in people who are allergic.
The fungus is growing in homes that didn't dry out. Other people tried to get rid of the mold, but the treatment didn't work.
That means people who waited to do repairs or couldn't get to their house for weeks are having mold problems.
Getting rid of mold can cost as much as $15,000. Federal emergency aid doesn't cover mold removal.
Officials in New York announced a $15 million program that will remove mold from at least 2,000 homes.