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What is the Scope of Computer Forensics?
Jety asks: "I do general-purpose tech support for a variety of individuals and small businesses. Today, one of my clients presented me with an interesting situation, which made me recommend that he get his own attorneys and computer forensics experts on the job. Above and beyond that, to satisfy my own curiosity and to have some insight to offer him in the meantime - I have some question about the scope of what computer forensics can accomplish, for this I turn to the experts of Slashdot, which can be boiled down to one issue: What exactly can a good computer forensics guy pull off of a hard drive - particularly once it's gone on to be used for a full week after the incident in question?"
"The sanitized details of my client's situation:
- Person A (my client) and Person B are business partners. Person A leaves the business, and before doing so copies a series of files to 5 CDs using Roxio under Windows XP.
- The computer continues to be used under normal circumstances for about a week.
- Person B confronts Person A, and Person A hands over the CDs to Person B.
- Person B hires a computer forensics 'expert', who claims that Person A accessed something like 3000 files during the 1 hour time span in question, when Person A was burning files to CD.
- Person A primarily wants to prove that the data he turned over on CD was the only data he took, approximately 50 word/excel type files, which we will assume to be true.
How detailed a record of file use does NTFS or WinXP keep? Can you really show what files were accessed during a one-hour time span seven days ago? Above and beyond the 'last modified' date? On a read/write/execute basis? Accessed by the system or by a user? Do commercial burning programs keep a record of burn jobs they've performed? Does the CD drive itself have any appreciable nonvolatile cache? Is there any other general insight applicable to this situation?"
- Person A (my client) and Person B are business partners. Person A leaves the business, and before doing so copies a series of files to 5 CDs using Roxio under Windows XP.
- The computer continues to be used under normal circumstances for about a week.
- Person B confronts Person A, and Person A hands over the CDs to Person B.
- Person B hires a computer forensics 'expert', who claims that Person A accessed something like 3000 files during the 1 hour time span in question, when Person A was burning files to CD.
- Person A primarily wants to prove that the data he turned over on CD was the only data he took, approximately 50 word/excel type files, which we will assume to be true.
How detailed a record of file use does NTFS or WinXP keep? Can you really show what files were accessed during a one-hour time span seven days ago? Above and beyond the 'last modified' date? On a read/write/execute basis? Accessed by the system or by a user? Do commercial burning programs keep a record of burn jobs they've performed? Does the CD drive itself have any appreciable nonvolatile cache? Is there any other general insight applicable to this situation?"
A side note, even if you can verify that the cd's he gave back contain all the data he took from the company computer. There is nothing to stop him from having made copies of those cd's when he got home.
Way back in the day (early/mid 1980s) I did a job like this.
Person A left company AA and started company BB then started taking customers. Attorney for AA got a court order allowing inspection of all magnetic media. Of course, by the time I was allowed access to the drive, several months had passed during which time "something had gone wrong with the computer" and "I think the repair shop had to format one of the drives". Yeah, right.
In any case, they thought that a basic reformat of a DOS hard-disk removed all the data. As I started pulling off and saving directory-fragments and disk sectors which showed that they had illegally installed specialized and unusual software belonging to the former employer as well as lists of names of clients they made fundamental mistake #2 - they started blabbing "explanations" for the data I was recovering. As a former law-enforcement employee I simply listened attentively to their stories...and included the additional incriminating evidence in my report.
Never even had to go to court and testify.
Things are more complicated, today. You are right to get a computer forensic expert involved. Many of the disk-recovery services like Drivesavers provide forensic services in addition to data-recovery.
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"You are not remembered for doing what is expected of you." - Atul Chitnis
How detailed a record of file use does NTFS or WinXP keep?
Pretty detailed. User account, time at a minimum.
Can you really show what files were accessed during a one-hour time span seven days ago?
Yes.
Above and beyond the 'last modified' date?
Yes.
On a read/write/execute basis?
In a roundabout fashion. I'm not as familiar with NTFS as I would need to be to give a good yes or no or yes with limitations. It keeps records of modification (write) and access (read) so the only unknown is whether one could tell if a file was merely read or executed. It is a journalling file system, so depending on how exactly it performs journalling, it may even be possible to find out which parts of a file were modified in the case of writes. This is less likely as journal records are, presumably, overwritten with new records over a short period of time.
Accessed by the system or by a user?
If I remember correctly, NTFS does record the date of creation, modification, and access with the user performing each action. Many "system" actions are performed in the user's name since, technically, the user is running the system program.
Do commercial burning programs keep a record of burn jobs they've performed?
Many programs do keep a short log of actions. They won't necessarily detail files involved, though. You'll be lucky if such a log tells you how much data was written to the disk in MB. This might actually be just as useful.
Does the CD drive itself have any appreciable nonvolatile cache?
No.
Is there any other general insight applicable to this situation?
Yes:
Person B hires a computer forensics 'expert', who claims that Person A accessed something like 3000 files during the 1 hour time span in question, when Person A was burning files to CD.
This points to a very simple search of all files modified, accessed, or created during that time period. Please note that this could indicate a virus scanner or system backup utility running in the backup as much as it indicates a cd writing program. Viruses can also exhibit this behavior. Try to find out how many files were accessed in the previous 24 hours before this particular hour, and the following 24 hours. It could be that every hour during that time had several thousand files uniquely accessed.
Person A primarily wants to prove that the data he turned over on CD was the only data he took, approximately 50 word/excel type files, which we will assume to be true.
Quite frankly, if he needed 6 CDs to burn 50 word/excel files... well, let's just say that you should explain to him that you try to assume nothing so that you can have the best view of the facts.
Also note that if data backups are made of the computer on a daily/weekly/regular basis, it may be that one can use those to show useful data about your client's use of the computer. An interesting tactic would be for your client's attornies to request a detailed log of computer use for the week previous and the week following the incident to establish a pattern of use. Request all possible backups. Request... well, everything. The attorney will know what you mean.
Lastly, keep in mind that your client has already 'confessed' - the only thing left to determine is not whether he is guilty, but how guilty. Chances are good that even if he didn't do more than he says he will have a hard time proving that he has fully complied.
Lastly: Don't become personally involved, or emotionally invested. Your client will be, and he may even be pulling you into it without knowing it. Understand that anything you say to him may be used in any forthcoming legal case, and you may find yourself more involved than you desire to be.
-Adam