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.
Allow F-Secure Anti-Virus to disinfect the relevant files.
For more general information on disinfection, please see Removal Instructions.