Don't worry about the XP machines at this time.. It sounds like they're working correctly, Yes?
And just curious, do you have Service Pack 2 installed on your Vista machine?.. If not, you should.
"Explorer" is not the browser.. That's "Internet Explorer" and is another file name.. Explorer is the the basic Windows Shell which causes the desktop to load, Windows "Explorer" to open when you open any folder, etc.
So, on the Vista machine, follow all of the procedures below to run multiple free malware removal tools:
If you can download the tools below on your current computer, and get them to work, then fine, but frequently the problem malware prevents the programs from running correctly. If that's the case, then download ALL of the tools below on a friend or family member's, CLEAN computer and copy them to a CD or flash drive, then transfer them to the problem machine and use them while in Safe Mode.
After transferring it to the problem machine, run the following tool to help allow the removal programs below to run. (courtesy of Grinler at BleepingComputer.com)
There are 3 different versions. If one of them won't run then try to run the other one. Be patient.... as a black window should open, then close after finding all the background programs.
Vista and Win7 users need to right click and choose Run as Admin
You only need to get one of them to run, not all of them.
IMMEDIATELY after running the "Rkill" tool above, run/install the Malwarebytes and SuperAntispyware installer and update files from the links below which you've also copied to a CD or flash drive, and transfered to the problem machine. Do NOT restart the computer after running Rkill.
Once downloaded and before transferring Malwarebytes and SuperAntispyware to the problem machine, rename the program installer "mbam-setup.exe" file to something else like "Gogetum.exe", then copy the installer file and the update file to a CD or flash drive.. Transfer the file to the problem machine, then install the "Gogetum.exe" file, then run the update to get the program current.. After that, run a full system scan and delete anything it finds.
Malwarebytes Installer Download Link (Clicking on the links below will immediately start the download dialogue window.)
Malwarebytes Manual Updater link
Next, install and run a full system scan with the SuperAntispyware program and the manual updater from the links below. As before, you may need to rename the installer file to get the program to install.:
SuperAntispyware Manual Updater
In a few situations, in order for the program to run, it was also necessary to rename the main "mbam.exe" file also after installing it.. It resides in the C:\Programs Files\Malwarebytes Antimalware folder....
And after that, if everything's fine by you can't connect to the internet, then follow the procedures below to check your network "proxy" settings again.
Open Internet Explorer and go to Tools-Internet Options-Connection Tab. Click on the LAN settings button. IF there is a check mark next to "Use a proxy server for your LAN", uncheck it. Click OK. Then OK, again.
Once that's done, run an online scan using the free ESET online scanner from the link below.. Click on the link to immediately download the online scanner installer, then let it run the online scan and remove anything it finds.
NOTE: Clicking on the link below will immediately open the download dialogue window.
ESET Online Scanner
Hope this helps.