Shortly after installing Firefox 18.0.2 on a Windows 7 system, Firefox aborted and had to be restored ("Well this is embarassing..."). I uninstalled 18.0.2 using the Windows "Programs and Features" controller. I then downloaded the 18.0.2 installer from www.mozilla.com, which re-directed me to "http://www.mozilla.org/en-US/firefox/new/", which I saved to my Desktop as "18-0-2_com". Windows complained that the file was not safe, although the most current version of Norton Internet Security, version 19.9.1.14, judged the file to be safe. When I ran the installer, Windows said the file was corrupt and stopped the installation. Next, I went to www.mozilla.org, which re-directed me to a different site, "http://www.mozilla.org/en-US/products/download.html?product=firefox-18.0.2&os=win&lang=en-US". I saved the file as "18-0-2_org". Windows did not complain about the safety of this file, and it installed Firefox 18.0.2 without incident. Since I run Cygwin 1.7.11-1, I was able to run the cksum command on both installer files. Here are the results: Source Local file name File length CRC cksum -------------------------------------------------------------------------------------------------------------------------------- mozilla.com 18-0-2_com 20300952 3466106289 mozilla.org 18-0-2_org 20300952 1844093656 Although both installers have the same length, they differ in content; consequently, the checksums differ. It appears that 18-0-2_com is corrupt, while 18-0-2_org is not. Since the two files come from different locations, it seems that one has been accidentally or intentionally altered. Since the file lengths are the same, I am suspicious that the corrupted file has been made to look like the uncorrupted file, so that the number of bytes in both files is identical. This suggests that the corruption was deliberate.