Burning CD files. Why is it sometimes all of the sudden the CD capacity is used up when minutes ago it's 10%?

Question

I have a CD-RW disc and downloading similar files of about 10k. The properties data showed only about 10% of capacity used. Then, for some reason, I get a message unrelated to downloading files, like using a word program, and the computer freezes. I then rebooted but lo and behold when I open my CD drive, the capacity is now 100%. How do I prevent this from happening.
How can a 10% used up CDRW be all of a sudden 100% used up without downloading another file. I did not load a large file to use up all of 700 MB.

Answer 1

Sounds like a Virus to me , run a virus scan, lots of free ones on internet

Answer 2

Burn in http://pclinuxos.com using k3b or gnomebaker. no coasters, virus proof.