All data operations are logged to the SQL tables:
dbo.AUDIT_LOG_DATA and
dbo.AUDIT_LOG_TRANSACTIONS
The logs are produced using the product "ApexSQL Audit" that generates triggers on all relevant tables to log any data change, no matter what the source of the change.
As the data updates are technically being performed by the ISS Application Pool user, all transactions performed through the web-server will be tagged with this user. However, all records have a "LastEditorName" field that is part of the logging so that the actual user can be tracked.