How to track an action when user creates a node of a specific content type?
I would use the Rules module, which allows for dozens of variations of tracking. As an example, here is a prototype of a rule, in Rules export format, to illustrate the possibilities:

{ "rules_find_links_in_body" : {
    "LABEL" : "Find links in body",
    "PLUGIN" : "reaction rule",
    "OWNER" : "rules",
    "REQUIRES" : [ "rules" ],
    "ON" : { "node_insert--article" : { "bundle" : "article" } },
    "IF" : [
      { "user_has_role" : {
          "account" : [ "site:current-user" ],
          "roles" : { "value" : { "2" : "2" } }
        }
      },
      { "OR" : [
          { "text_matches" : {
              "text" : [ "node:body:value" ],
              "match" : "http(|s):\/\/+",
              "operation" : "regex"
            }
          },
          { "text_matches" : {
              "text" : [ "node:body:value" ],
              "match" : "ANotAllowedTextStringInBody",
              "operation" : "regex"
            }
          }
        ]
      }
    ],
    "DO" : [
      { "drupal_message" : { "message" : "Node body contains an URL ..." } }
    ]
  }
}


Some more details about the above prototype rule:


Rules Event = After saving new content of type "Article" (adapt the type to fit your needs).
Rules Conditions:


Check if the current user is an authenticated user.
Perform a text comparison, using a Regular Expression as the Comparison operation (which you can perfectly do in Rules, without using the PHP filter for it). For the actual regular expression, this rule uses http(|s)://+, which will discover strings that start with either http:// or https://. Should you have additional / similar requirements to discover variations of this (say some other string like ANotAllowedTextStringInBody), another Rules Condition (with an OR) will take care of that also.

Rules Action = Show a message on the site (adapt the message to fit your needs), and/or add other relevant Rules Actions ... Such as:


use the Message module as illustrated in the answer to "How to log and display all the users that have edited a node (without revisioning)?".
send an eMail, either to a specific user, or all users of a specific role.
use the Flag module to flag the user (for whatever reason).
grant a special role to the user.
... (the possibilities are only limited by your own imagination).



Voilà, easy as that ...