As Vinylpusher mentioned, they are compressed or encrypted files. Windows NT/2000/XP have a built-in compression driver, that can automatically compress/decompress files when you write or read them, in order to conserve diskspace. This is pretty much transparent to the average user.
The advantage: smaller files = more usable diskspace
The disadvantage: your computer needs to do more work (compress/decompress) the files in the background, meaning that these compressed files are slower to handle than uncompressed files.
If you right-click -> Properties on these blue files, you can see both the 'real' size (the amount of data that the file contains) and the size on disk, which is how much diskspace the actually file takes up after it was compressed.
The windows disk cleanup utility which can kick in if you're very low on space can start compressing files that aren't changed very often, which could explain how they started to appear in blue all of a sudden.
3rd party system optimization programs can do this as well for you.
Now, as mentioned above it's also possible that the files are encrypted.. This can be good if you want to protect your data from unauthorized access, other users on your computer won't be able to read the contents of the file in question if they happen to come across them. If you put the harddrive in a different computer, it won't be able to read the file either.
Secure, but also a potential major headache if your operating system dies on you and you try to recover your data -- you won't be able to access it without the embedded security key in your XP profile, which you need to remember to export to a safe location to regain access to those files again when doing disaster-recovery...
so if you're using the encryption deal: just be careful, and make sure you back up the key as well... but most likely you'll find that you simply have compressed files on your computer, and not encrypted ones.
The advantage: smaller files = more usable diskspace
The disadvantage: your computer needs to do more work (compress/decompress) the files in the background, meaning that these compressed files are slower to handle than uncompressed files.
If you right-click -> Properties on these blue files, you can see both the 'real' size (the amount of data that the file contains) and the size on disk, which is how much diskspace the actually file takes up after it was compressed.
The windows disk cleanup utility which can kick in if you're very low on space can start compressing files that aren't changed very often, which could explain how they started to appear in blue all of a sudden.
3rd party system optimization programs can do this as well for you.
Now, as mentioned above it's also possible that the files are encrypted.. This can be good if you want to protect your data from unauthorized access, other users on your computer won't be able to read the contents of the file in question if they happen to come across them. If you put the harddrive in a different computer, it won't be able to read the file either.
Secure, but also a potential major headache if your operating system dies on you and you try to recover your data -- you won't be able to access it without the embedded security key in your XP profile, which you need to remember to export to a safe location to regain access to those files again when doing disaster-recovery...
so if you're using the encryption deal: just be careful, and make sure you back up the key as well... but most likely you'll find that you simply have compressed files on your computer, and not encrypted ones.