The answer is C, they are not always illegal, and they are not always legal
First, ask friends and family if they have gotten infected by a possible virus (It is most common on .exe files)
Seccond, use a file scanning service like spybot or Avast to check to see if the file is infected, if so, delete it ASAP
Third, good luck with web safety
Matches a string that has both the substring dog and car in the string in either order