I have found at least six Windows PCs on my network that have one or more copies of a file where the entire file name is "~", no extension. Naturally I don't have one at my fingertips, so I can't give more details.
The usual locations are: root C:, Desktop, My Documents, Windows. The file(s) are always dated "today". If I delete the file, it shows up again next time I remember to look days later.
The PCs all have some version of Windows, Norton Corporate Anti-virus, and at least one has had Ad-Aware run on it multiple times.
I am not sure if this is connected with mal-ware or not, or even what the dickens it is!