I tried installing antivirus on my system because my sister complained that there was no anti-virus in it. When i inserted an avast anti-virus software, it first passed the first, second and third page then it disappeared, i tried it several times but still the same.
Some malware can prevent the installation of programmes it knows can destroy it so your system may already be infected. Go to http://www.malwarebytes and download MalwareBytes. Install and update it then restart your computer into Safe Mode with Networking by tapping the Function 8 key before Windows gets a chance to load.
MalwareBytes or MBAM for short, might want further updates and that's why you need the networking running. When it's finished, click to run the Full Scan and when that completes, click on Show results and then on Fix Selected. Restart again and do nothing this time so it goes into Normal Mode and you should be in the clear but if that file shows up again, go back into MBAM and scan in Normal Mode and also click the Logs tab then copy and paste the Safe Mode log back here for more advice.
Don't forget to retry installing Avast before you spend too long online even if MBAM has cleared some nasties out.