The virus itself is very simple and will never become a real-world problem.
The Donut virus is 8kB long. When executed, it infects all other .NET executables with .EXE extension in the current directory and directories above it.
After this, there's a one-in-ten chance the virus will show a dialog box with this text:
This cell has been infected by dotNET virus!
.NET.dotNET by Benny/29A
The virus will then just exit. It doesn't stay in memory and will only spread further if an infected file is executed again.
The first fully .NET compliant operating system from Microsoft, known as 'Blackcomb', is estimated to ship in 2003.
Donut has not been found in the wild. It is not considered to pose any threat at the moment. Nevertheless, it's the first virus of its kind.