To get the details we have to configure the SharePoint 2010 audit settings
§ Go to Site Actions > Site Settings > Site Collection Administration > Site Collection Audit Settings
§ Click Editing Users and Permissions.
§ Click OK
Now to run the audit report:
§ Go to Site Actions > Site Settings > Site Collection Administration > Audit Log Reports
§ Click the link for Security Settings under Security And Site Settings Reports
§ Select a location where the spreadsheet report will be stored. In my case, I just used the Shared Document library.
§ Click OK.
The report will churn away for a short bit and save the spreadsheet when its done. When you go into the location where it’s saved, just click on the file and Excel will launch.
There are two sheets in the report. The first is summary information (which wasn’t of much use to me), and the second sheet is the detail. You’ll quickly see that the information will never be mistaken for “user-friendly”, but you can dig through and find who added, deleted, or updated permissions to the site. It doesn’t tell you what was added or changed, but at least it gives you a general guide to who has been making updates and when they occurred.