Active Directory stores users’ last logon dates in lastLogon attribute and last successful password set dates in pwdLastSet attribute. You may think that it’s as easy as running an LDAP query to get these values. Unfortunately, it’s not that simple.
Background
If you check these values in ADSI Edit tool, you will see a well formatted timestamp. However, if you double click it, you will see a long integer. This is the value your .NET code will receive through an LDAP query. Active Directory returns dates as Int64 data type.
Solution
In order to convert Active Directory’s Int64 timestamps to .NET’s DateTime format, use the following code line.
DateTime lastLogon = DateTime.FromFileTime((long)oSearchResult.Properties["lastLogon"][0]);