Log in via your sisters account and try the following - it may not be malware, but it might.
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Use these to remove Malware (Spyware and Adware).

1) SpyBot Search and Destroy
After installing SpyBot Search & Destroy, first press Online, and search for, put a check mark at, and install all updates.
Next, close all Internet Explorer windows, hit 'Check for Problems', and have SpyBot remove all the items it marks in red.

2) Get Ad-Aware
After installing Ad-Aware, and before running the program, first press “check for updates now".
Click "Connect" and install all updated components available. Click 'Finish'.
Press "Scan Now", then 'next', and let Ad-Aware scan your drives.
It will find a number of "bad" files and registry keys. Click 'Next' again.
Check all found items, and click 'next' once more.
It will ask you whether you'd like to remove all checked items. Click OK.

Always reboot the computer between each program - both of these may find things that they need to have a reboot of the machine to clear - please reboot and let them finish .

Failing those solving your problems a post of a hijackthis log for the experts to advise.
HijackThis From Here
Important: Create a folder on the C: drive called C:\HJT.
You can do this by going to My Computer (Windows key+e) then double click on C: then right click and select New then Folder and name it HJT.
Unzip HijackThis into this folder. When you run HijackThis from this folder and have it "Fixed checked" it will create a backup file of modifications to use if restore is necessary. Then run, scan, save log, then in notepad copy the FULL log by copy and paste as a reply to this post and an expert with HijackThis Knowldge, will have a go at giving advice. Please note the list of experts names below, very few forum regulars here have had this training.

DO NOT FIX ANYTHING WITH HIJACKTHIS WITHOUT EXPERT ADVICE, most of what it finds you need for normal MS Windows tasks.

Known Spyware HijackThis fighters in DellTalk - If you are, and are not on the list please PM Me.

TomCoyote (of http://tomcoyote.org/forums/index.php fame)
YoKenny (Accredited Expert at TomCoyotes)
baskar1234 (Spyware Classroom Teaching Assistant at TomCoyotes)
ChrisRLG (Spyware Classroom Teaching Assistant at TomCoyotes)
Yellowhammer (In Training at TomCoyotes)
therock247uk (In Training at TomCoyotes)
irelynmisses (In Training at TomCoyotes)

You could also go to one of the more specalist forums where more experts will be able to help.
http://tomcoyote.org/forums/index.php
http://forums.spywareinfo.com/index.php
http://www.net-integration.net/cgi-bin/forum/ikonboard.cgi (Home of Spybot S&D)
http://boards.cexx.org/index.php
Do read the sites FAQ before posting, and advise your problem and what steps you have already done to try to cure your problem.

I, and the other hijack experts mentioned above, are in all those sites (and more) with the same login names. You might get one of us at those sites also to anwser your log, but other experts will also be available.

Dear Blackie,

 

  Just wanted to clear some things up.  They did not mention using spyware software, my mistake.  Still, just trying, as a friendly computer user to offer some helpful advice.  The advice I gave, no one else had mentioned, so I thought I would.

I didn't see where the OP mentioned that they used AOL, so that solution could very well be unattainable.  Further, ChrisRLG, a forum regular, gave the correct advise.  There's zero harm in running spyware detectors and the HiJackThis application typically reveals any viruses or trojans running.  I'd be willing to wager that 90% of computers lacking spyware protection do have spyware on them.  Anti-virus programs won't find those and neither will AOL's program.

Dear Blackie,

  I was just offering advice.  I have NoAdware installed on my computer.  In fact I would advise everyone to use some kind of spyware software.  I did not mean to imply otherwise.  I just offered some advice that I thought might be useful.  She did not say she used AOL.  But she did say she had tried some spyware software to solve her problem and it did not work.  No offense to anyone.