I’ll make this process easy for you, by providing a couple of useful tools.
This list is going to be expanded and edited from time to time.
Online Information Gathering Tools
Have I Been Pwned
Have I Been Pwned is one of the online information gathering tools. It
It lists all the events in which the information has been leaked, so you can search for the dump of the specific event.
Check usernames is another online tool.
It’s more of a fun gimmick to get the gist if a user uses the same username on different platforms.
You can (ab)use this information to get more information about the specific user.
Information Gathering Search Engines
Shodan.io is a search engine for (ethical) hackers. You can search for specific IP’s, Ports and services to find open (and vulnerable) services
TheHarvester is a CLI- tool that automates the process of “google-ing” information like emails, phone numbers and DNS settings for a specific domain, using the search engine of your choice.
Nmap is one of the most well known information gathering tools around.
It’s an advanced port
Masscan is a TCP port scanner that is able to scan the entire internet in 5 minutes. Or so it claims.
Netcraft is a tool similar to BuiltWith. You can get information about the hosting provider, DNS, WhoIs and more information using it.
Security Trails is another web- scanner, listing multiple information like DNS- Records, subdomains, history data and more.
It also exposes sites behind Cloudflare.
Urlscan.io is another web-scanner.
It focuses on how many ads are around, how much percentage of the site is in https, domains, subdomains, countries, size, cookies and more.
Informationg Gathering Visualization
Maltego CE is an information gathering tool, that includes a very stylish UI. It will remind you of the Microsoft Office Suite.
There is a free community version available, with which you can draw graphs of different information and the relations to each other. You can check out an example in the video above.
More info about information gathering and ethical hacking can be found in this article.