Once every 6 months or so, I do get a virus. I came across this one from Limewire.
Symptoms: regedit, cmd & task manager lost! "in use by another program"
After using Ad-Aware and Microsoft Defender, my system was reported as clean; only clearing out some cookies.
Several sites report the problem: Cannot open task manager; task manager fails, regedit and cmd same issue.
The virus takes hold of these application pointers, fortunately I use an application as a replacement for command prompt so I was able to source the issue.
Two files need to renamed/deleted:
b.exe (in Windows root folder) and svchost.exe located in Startup. The virus uses a trusted name (svchost.exe) but puts the file in the Startup folder.
I don't use any memory resident virus prevention software. I rarely come across malware, however when looking for a software crack, questionable software, or the like. In this case, I downloaded something from Limewire. Many of the listings on Limewire these days are viruses and such, so you do need to be careful. I believe the software operates as a Limewire distributor for the virus itself. I cannot find anything it does beyond redistribution of itself.