I get an "Install now" window during Windows XP SP2 start-up. It says: "Critical security alert - software removal". The only buttons offered are Delete all, Remind me later and Install now. It first appeared as an alleged update for Adobe Reader 7.0. Iain Main
This appears to be legitimate. Adobe is trying to get users to update Adobe Reader because "critical vulnerabilities have been identified in Adobe Reader and Acrobat 7.0 through 7.0.8 ... although Adobe is not aware of any specific code exploits at this time". For details of fixes, see Adobe's security bulletin at http://www.adobe.com/support/security/bulletins/apsb06-20.html
Adobe recommends upgrading to Adobe Reader 8. This is a somewhat hefty download -- 20.8MB from http://www.adobe.com/products/acrobat/readstep2.html -- so you might want to consider an alternative way to read PDF files. Foxit Reader 2.0 is much smaller (about 1.5MB), simpler and faster, can convert PDF files to text, and is also free for non-commercial use. However, it only works with Windows. Download it from http://www.foxitsoftware.com/pdf/rd_intro.php