When users share files on P2P networks, using software such as eDonkey or Gnutella, they often just wind up sharing the entire C: drive. This makes it possible for the wouldbe spammer to get hold of the user's Outlook.pst file, where their Outlook messages are stored. All they have to do is search for "Outlook.pst" on the P2P network, and once some files are obtained e-mail addresses can be extracted.
Experts from Blue Security, who discovered harvesting, have carried out an experiment to evaluate the efficiency of method.
The experiment consisted in creating a list with 500 e-mail accounts, real but not used, that was saved in such file, Outlook.pst, and shared in a P2P network.
In the first day, these addresses received 100 spam messages, next day the number had reached 300. Even after two weeks, the addresses continued to receive 100 spam messages a day.