There is a virus being reported by a couple AutoCAD based product customers. The original virus first popped up in 2005 and was very limited but has been changed slightly. Some antivirus software does detect this virus and remove it. Many great people worked behind the scenes over the past week to research and publish a solution.

The virus spreads simply by someone placing the malicious acad.vlx in a directory with the DWG files or a support path location being opened  and then spreads from there into open DWG files and by replicating itself.

The below LISP code detects and deletes any acad.vlx file before AutoCAD attempts to load it, preventing the spread of the virus. The possible random strings written to the DWG file by the acad.vlx appears to be harmless.  The malicious file acad.vlx is not an Autodesk file.

The Autodesk Technical Solution being published.to the AutoCAD Support Page and also being mentioned on the Support Blog - Without A Net by Tom Stoeckel:

ID: TS13717811
Published date: 2009-Aug-07
http://usa.autodesk.com/getdoc/id=TS13717811

Issue

Users of AutoCAD-based products have reported a malicious acad.vlx file that causes drawing corruption.