As I know you can do Denial of Service when footprinting with scanners, like nmap or Maltego. But is it legal? As I know, scanning isn't illegal but doing DoS attacks is.

EDIT I meant if you scan just random sites with no relationship with it.

  • Where ? Against what target ? What's your relationship with the target ? How exactly are you performing a scan ? How does that lead to a DoS ? This question doesn't have a general answer
    – Stephane
    Oct 8, 2015 at 8:41
  • Edited, p.s. - any kind of scan - service scan, crawling etc Oct 8, 2015 at 8:52
  • This is a legal question: you've asked a legal question that varies from country to country (scanning is illegal in some countries), and you've asked a "mens rea" legal theory question.
    – schroeder
    Oct 8, 2015 at 14:49

1 Answer 1


Unwanted DoS by portscans is kind of a myth. A simple CONNECT or SYN scan (ab)uses TCP functionality to find out if a port is open or closed. This won't be a problem for the running daemons because thy almost surely leave it to the operation system to handle the resulting events. The only way a daemon has to handle these itself is when the developer used RAW Sockets.

When it comes to more extended scans that for example are used to guess which operation system is running on a host it can theoretically cause problems to very old or poorly configured hosts. This is because OS guessing is (beside other techniques) done by causing unusual situations to the host which then has to react. These reactions in many cases are specific to a TCP/IP Stack implementation which can be attributed to an OS or a Kernel Version,...

What really can get dangerous is using a vulnerablity scanner linke nessus without the needed knowlege and/or care. There are thousands of modules and some of them can cause a DoS (and they are labeled as those) to the scanned system.

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