Why is my computer suddenly very laggy after a recent reboot?

Question

My computer worked perfectly fine until a recent reboot. I normally reboot every week or so. But this time, the computer feels very laggy.

By laggy, I mean the Windows Explorer open and close animations are slow. Moving a window around is slow. Typing and clicking are slower than usual, but the mouse movement is fine. Trying to run a game where I normally get 30-40 fps in drops down to 1 fps and doesn't even make it to the title screen.

I have run multiple anti-malware scans from various programs, from Malwarebytes to TDSSKiller. Found nothing.

I have unchecked needless startup processes in msconfig. No results.

There were no recent changes, installations, or updates.

Check Disk, System File Check, and Windows Memory Diagnostic found no issues.

The CPU, RAM, I/O, and graphics usage percentages are all normal. No overheating.

Safe Mode runs normally, but I don't know if that's because the cause isn't happening or if Safe Mode is much lighter on resources.

• Windows 7 Home Premium 64-bit SP1
• 3.4 GHz Intel Core i7 processor
• 8 GB RAM
• Nvidia GeForce GTX 550 Ti graphics card
• 128 GB SSD, 100% healthy according to Hard Disk Sentinel

What could possibly be happening, and what can I do to fix this?

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Note: I bolded key words for TL;DR and quick glance purposes.

Answer 1

The problem turned out to be a service called NVU. Its description claims it to be the "NVIDIA driver updater". The file itself is "C:\Windows\nvidia\wintask.exe". I emailed Nvidia about it, and it does not belong to them.

It turns out the sister program, NvUpdater64.exe, is a virtual currency miner. Both of these files are located in C:\Windows\nvidia.

I have submitted them to a few anti-malware companies.