This virus first adds 1-16 bytes to the files it infects, so they end on a paragraph boundary. Then 669 additional bytes, containing the virus itself are written to the end.
On any Saturday the 14th, the first 100 logical sectors of drive C, then B, then A are overwritten with rubbish.
Once detected, the F-Secure security product will automatically disinfect the suspect file by either deleting it or renaming it.
Detailed instructions for F-Secure security products are available in the documentation found in the Downloads section of our Home - Global site.
You may also refer to the Knowledge Base on the F-Secure Community site for further assistance.