If an attachment is opened the computer becomes infected, and on the third day of every month it will seek and delete file types on Windows computers including Adobe PDFs, Microsoft Word, Excel and PowerPoint documents.
It even tries to disable out of date anti-virus software.
BlackWorm's spread is said to be relatively low compared to other viruses.
Computer giant Microsoft has warned customers to make sure they have the latest anti-virus software and that it is turned on.
Users should also check the date on their computer, because if its calendar is wrong files could be destroyed sooner or later than the virus' schedule.
