Disregard comment#9, and total b*llnuts!
This is one fantastic piece of software, and good e.g. in movie archiving: DivX -certified players play movies encoded with XviD, you can put as many as six on a single DVD without any noticeable quality loss.
Of course, x264/h264 is more modern; more efficient in compression with better picture quality, but not as well supported by players as DivX/XviD. And DivX is commercial, which means you should pay for something you get for free anyway, and don't even have to break any laws ;)
So download this one, support open source software (or good sw at least) and start encoding!

I just downloaded this codec and everything seems okay, I can now watch video with my audio and no virus notices have popped up.

Very good freeware codec, easy to install.

I use this codec to encode films in AVI format with VirtualDub. The XviD configuration is made for experts and provides users with useful settings to experiment with. It includes a Bitrate Calculator which lets you enter a desired target size (in kbytes) and calculates the according target bitrate (in kbps) to match the filesize as near as possible. The same can be done for audio bitrates.

For example, a DVD film with a common length of 90 minutes can be compressed into a target filesize of 665600 kbytes (650 MB) or 716800 kbytes (700 MB) only! Such a video file could be stored on a single CD-R. The balance between compression ratio and image quality is excellent. Even at lower bitrates and higher compression the results are sufficient.