It is not illegal (in the US, but keep in mind not everyone on this site is US-based nor are the companies that might get targeted by a spider written here).
However, it may be unethical.
"Please don't do this to our site and our property and our data."
"Yeah, well, screw you. I'm doing it anyway."
For further actions, you may consider blocking this person and/or reporting abuse
We're a place where coders share, stay up-to-date and grow their careers.
It is not illegal (in the US, but keep in mind not everyone on this site is US-based nor are the companies that might get targeted by a spider written here).
However, it may be unethical.
"Please don't do this to our site and our property and our data."
"Yeah, well, screw you. I'm doing it anyway."