In a range of fields (I have in mind gender and sexuality) users make Internet comments revealing personal details about themselves. Some sites even automatically link to their personal Facebook page. While this data may be useful for research, there are ethical issues as to how to use this data.
On one hand, they have voluntarily published this material online, and made it accessible to the world.
On the other hand, presumably the audience they had in mind for their post is likely to be limited a handful of users. It is personal information that could potentially be used against the user.
Question: What are sensible measures to ethically use freely available, but personal web-based comments in research?