Account unknown(S-1-5-5-0-649118)

For example, when i download any word document file from internet to my laptop. After downloading the word document to my laptop, i right click on the word document - properties - security.

Here i am seeing Account unknown(S-1-5-5-0-64911 is created. This is happening for not only downloaded files but also if i create any new folder or new file on my laptop, this Account unknown(S-1-5-5-0-64911 is assigned to those newly created folders/files.

Please let me know if you need any more information.

Thank you for your help.

With me here, I only see 4 lines in the "Groups and users":
- Verified users
- SYSTEM
- Administrators
- Users
What do you see?

It looks like the interal code of some Windows account or so that you deleted. Since it doesn't seem to exist anymore, I shouldn't worry about it having certain access permissions to your files.

Kees

than you should be telling us about your specific internet and network configuration we are going to have to let you discover your own DEFINITIVE answer. This link should help:
http://support.microsoft.com/kb/243330

For a simple answer I personally would say to ignore it and not worry about it because the S 1 5 5 0 indicates an NT Authority logon session SID (Security Identifier). This is a well known SID and is normal in Windows - it DOES NOT signify any security lapse or "hacking" or anything else of concern. Modifying access permissions though could cause some unforeseen problems with the files.