I have had my personal files encrypted using Windows XP's file encryption option for three years now. It's been working well until a few months ago when I suddenly lost access to all my files! That's almost all my personal and research data. Only some of them, maybe 10%, have backup files scattering here and there. Thank God, my family photos are not in there. This is mysterious. I have seen people lost access to their encrypted files from system re-installation, removing hard disk drive from the computer where the files were encrypted, something like that you lost your original OS. But I am not the case. I am still on the same system. The files are on an external drive. It's not moved, been like that all the time. What I found is that my certificate has been changed twice. I found this by looking at the encryption details in my files. You can see the thumbprint of the certificate that's used to encrypt the file in file properties ->advanced ->details even though you can't open the file. I could narrow down the time when the second change was made to a few hours, and the first change must have occurred shortly before the second change. Then I found out that the only program I installed during that time was Windows Defender! Is this possible? Windows Defender changing my certificate and causing me lost access to my files? Has anyone seen this before? - BWoods 1 person needs an answerI do too

Does anyone know if any program could change my certificate like this? If Windows Defender did this, is there any way to reverse it? Many thanks! ----------------------------------- I have had my personal files encrypted using Windows XP's file encryption option for three years now. It's been working well until a few months ago when I suddenly lost access to all my files! That's almost all my personal and research data. Only some of them, maybe 10%, have backup files scattering here and there. Thank God, my family photos are not in there. This is mysterious. I have seen people lost access to their encrypted files from system re-installation, removing hard disk drive from the computer where the files were encrypted, something like that you lost your original OS. But I am not the case. I am still on the same system. The files are on an external drive. It's not moved, been like that all the time. What I found is that my certificate has been changed twice. I found this by looking at the encryption details in my files. You can see the thumbprint of the certificate that's used to encrypt the file in file properties ->advanced ->details even though you can't open the file. I could narrow down the time when the second change was made to a few hours, and the first change must have occurred shortly before the second change. Then I found out that the only program I installed during that time was Windows Defender! Is this possible? Windows Defender changing my certificate and causing me lost access to my files? Has anyone seen this before? - BWoods