Credits source

This represent an application that contains data that can be stolen and sold for script credits. Selling the data will be performed automatically when you hack this layer.

You needs to have the Script credits skill to be able to steal the data, see here.

⇋ view 
Node service layers: 
0 OS 
1 Mailserver 

⇋ hack 1 
Valuable data found, worth 10⚡. Sending to data broker. 
Clearing data from layer... 

Done.

⇋ hack 1 
No data of value found. 
Logs indicate data has recently been deleted.

The data can only be stolen once, stealing it will remove the data from the layer.