My 6-months old computer has ever been infected twice, once by a trojan horse and another time by a rootkit. Both has been gotten rid off by my antivirus software.
I would like to know whether it is possible for computer performance to dramatically drop after a malware infection, even though the cause itself is no longer present.
OH...very much so...that's what malware, spyware and adware are known for. These are some of the top free software apps that most of us use here to get rid of such malicious software. The only way to be sure you truly got rid of it is to run this apps in safe mode with networking (so you can update the software if needed) do a full scan. This will take a very long time, 2 to 6 hours or longer depending on how much data you have stored on your hard drive and how infected the system is.
Spybot Search & Destroy
Malwarebytes
Ccleaner
SuperAnti Spyware
Adaware
Your antivirus software is not setup to find all this other stuff....that is, unless you have a paid subscription which has those addons. And even then one type of app/software doesn't find everything...if it did someone would be really rich. That's why we all use these types of programs in-conjunction with our Anti Virus program. And even then it's not full proof.
I have started with Safe mode, Malwarebytes and Avast scans didn't indicate any viruses/malware, and the problem went away while my computer is in safe mode. I am not sure if the malware is hiding at the moment or it has already went away.
Do you have all the latest MS updates and all the current drivers for your system including your mouse. I see that your using a logitech wired mouse....there is some software app for it.
Mouse M100
Refer my Post 11 where I asked...
List all the Security software you have ever had installed & currently have now on your computer please.
Quote