It's time to collect the info we'll need to tailor the cold content intended for prospects.
The data is entirely open source, which means it can be gathered from published or otherwise publicly accessible sources, thus it's perfectly legal.
The depth of your dive is only limited by how far you want to go - and the confines of what is acceptable and in good taste. Gather information that is relevant to winning work or getting a job, and don't include information about the prospects personal matters like family, wedding, pets, ill health etc.
That would be obsessive and pretty weird. Always remember that the information obtained on a prospect is used purely to start and maintain communication with them - and not to creep them out.
In addition to the info about them that’s already online, prospects post to social networks, blogs, communities, and sites everyday. As such the personal or professional details that can be found include: