The XA1 virus overwrites the beginning of files with itself and stores the original code at the end of the file. On April 1st, a part of the virus will activate - overwriting the boot sector with code that will cause the computer to "hang" on next boot-up. The virus will also activate on December 21st and stay active until the end of the year. It will then display a Christmas tree, and the text:
Und er lebt doch noch: Der Tannenbaum! Frohe Weihnachten
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.