Autodesk has released AutoCAD 2013 Service Pack 1 on August. But apparently there is an issue with the SP. AutoCAD keep crashing after SP is installed. A few days after they release it, they remove it from download page.
Now Autodesk release Service Pack 1.1. This SP should be free from earlier issue.
However, there is a note for Windows 7 installation in read me file. There is no explanation what will happen if we ignore the note, but based previous experience we better follow it.
Download AutoCAD 2013 Service Pack 1.1 here: http://usa.autodesk.com/getdoc/DL20327837
Remember to read the read me when you install a service packs or hotfixes. There are interesting new variable to control LISP in this Service Pack. I believe this can enhance security if you manage it well. As we know, there are computer virus/malware that works with LISP.
