Disconnect the contaminated system from the Internet.
Backup all documents, photographs, music, and other important user data,
if you are going to be re-installing the entire operating system.
Look in the event logs to see when any suspicious events happened, such
as the installation of remote control software for example.
Remove all remote control software and other programs that were
installed at the same time.
Go into System Properties and disable Remote Assistance connections.
Disable all remaining remote support capabilities (such as services upon
which programs like ‘TeamViewer’ and ‘LogMeIn’
rely.
Run Malwarebytes Anti-Malware (if you have difficulty running this
program then you will need to run MBAM Anti-Exploit first to kill
off self-protecting malware).
Reboot the system.
To increase coverage, run another program for removing malicious
software, such as Spybot Search & Destroy or
SuperAntiSpyware.
Update the operating system to the maximum possible extent, then update
all applications that are out of date and represent possible security
risks.
If official support for the operating system has ended, consider
installing an alternative operating system such as Linux Mint
alongside or in place of the outdated one.
Change all passwords, including those for logging in to the computer,
fetching and sending e-mail, connecting wirelessly to the router,
gaining administration access to the router, etc.
Log in to the router and check the DNS settings (they will probably
point to the Internet Service Provider’s DNS, but you could
set the primary DNS to ‘8.8.8.8’ and the secondary
DNS to ‘8.8.4.4’ to use Google’s
facilities).
Check that ‘/etc/hosts’ has not been contaminated (the
anti-malware programs run earlier should have done this, but it
never hurts to inspect this file personally).
Re-connect to the Internet, then download and install a good free
anti-virus program such as Avast Free Antivirus.
If you are limited for time, run a Smart Scan, but if you have plenty of
time then run a boot-time scan (it is a good idea, when running a
boot-time scan with Avast Free Antivirus, to allow the program to
download and install additional definitions before starting the
scan).
Use ‘autoruns’ to switch off any remaining suspicious
processes.
Use ‘services.msc’ to to switch off unnecessary services.
Use ‘CCleaner’ to remove unnecessary files and registry
entries.
Optionally use ‘BleachBit’ to remove even more unnecessary
files.