Hi fredlassiter88,
Welcome to Adlice.com Forum.
POST is a request method implemented in the
Hypertext Transfer Protocol (HTTP) application protocol. The data enclosed within a POST request is submitted from a web browser to a remote HTTP server.
Malware will usually install Browser Helper Objects (BHO) or Web Extensions to parse the content of the page on the fly and save the content of interesting fields within forms.
HERE is an exemple of a form using POST. Since forms often have many fields, malware usually filter the data to be stolen to interesting fields, like "username", "password", etc.
I don't known of any malware that capture all POST fields and data.
Regards.