Kinda hate to think what it could be because there are some very serious infections out there right now.
Since you didn't list which ones try the following.Do you use IE only or FireFox to?
Double click ATF-Cleaner.exe to run the program.
Check the boxes to the left of:
Current User Temp
All Users Temp
Temporary Internet Files
The rest are optional - if you want to remove the lot, check "Select All".
Finally click Empty Selected. When you get the "Done Cleaning" message, click OK.
If you use the Firefox or Opera browsers, you can use this program
as a quick way to tidy those up as well.
When you have finished, click on the Exit button in the Main menu.
Please download Malwarebytes' Anti-Malware to your desktop.....
* Double-click mbam-setup.exe and follow the prompts to install the program.
* Be sure a checkmark is placed next to Update Malwarebytes' Anti-Malware and Launch Malwarebytes' Anti-Malware, then click Finish.
* If an update is found, it will download and install the latest version.
* Once the program has loaded, select Perform quick scan, then click Scan.
* When the scan is complete, click OK, then Show Results to view the results.
* Be sure that everything is checked, and click Remove Selected.
* When completed, a log will open in Notepad. Please save it to a convenient location.
* You can also access the log by doing the following:
o Click on the Malwarebytes' Anti-Malware icon to launch the program.
o Click on the Logs tab.
o Click on the log at the bottom of those listed to highlight it.
o Click Open.
Tutorial if needed
If MBAM encounters a file that is difficult to remove,you will be presented with 1 of 2 prompts,click OK to either and let MBAM proceed with the disinfection process,if asked to restart the computer,please do so immediately.