Does anybody know?

Here are some resources where you can learn more about this pestiliferous phenomenon:
Information about spyware and adware, along with the current issue of the Spyware Weekly Newsletter [to which you can subscribe] is at www.spywareinfo.net
The major resource on scumware, which will also test your system for some common types of such pests, is at http://www.scumware.com/
Net vulnerabilities and find out news about security developments is at http://grc.com/default.htm
If some program is operating behind the scenes you can detect it with: Startup Monitor: http://www.mlin.net/StartupMonitor.shtml and Startup Control Panel: http://www.mlin.net/StartupCPL.shtml
A useful tool to combat such programs [as well as far worse programs which can be installed on your system to disable it or to be used to attack others is: Anti-Trojan: http://tds.diamondcs.com.au/ -- this is not necessarily the easiest to use or the cheapest, but it is the most thorough and has the best reviews for technicalability.
New, Free Online Firewall Test
http://www.auditmypc.com/ {Free online firewall tests} The site is promoting security awareness by offering free an online security audit, firewall test, and research center.
Other, similar sites:
Good And Bad Online Security Check-Ups:
http://www.informationweek.com/841/langa.htm
The Best PC Help, Reference, And Test Sites:
http://www.informationweek.com/story/IWK20010916S0021
Start-Up Applications Unplugged
It's frustrating trying to edit the Windows start-up list because the filenames themselves tell you little about the program's function. This free site lists thousands of common startup files along with full descriptions of what they do plus links back to the vendor's web site. Top stuff.
http://www.pacs-portal.co.uk/startup_pages/startup_full.htm
I hope this will help you