E-Virus (part I) How to recognize the symptoms of a E-FLU or if your PC has got an E-VIRUS?

E-FLU (Electronic Fluence) and / or E-VIRUS (Electronic Virus) gather all the endless series of softwares that infect the PC by self-replicating and / or consuming its resources (i.e.: malwares, trojan horses, backdoors, spywares, rootkits, dialers, worms, viruses, etc.). 

1) The PC is unexpectedly slow: suddenly the speed of execution of any application, even the most banal, it slows down quite sharply. In parallel we see that the hard drive is still active (the LED is constantly lit). The feedback of the mouse or of the keyboard could be slowed. 
2) Problems with the browser: the browser's home page (Internet Explorer, Firefox, Chrome, Opera, etc..) has changed and is pointing to illegal Web sites, or, by opening the browser many pop-up windows appear and replicate indefinitely. 
3) Internet is too slow: suddenly, surfing the Internet has slowed down. 
4) The PC is inoperable: The computer starts but stops immediately with messages like "missing operating system" or "could not find command.com". The PC frequently restarts randomly and unexpectedly. 
5) Modified files: Some files, especially those with the extension. ".exe", ".com", ".dll" have been changed and are larger than usual. The hard drive space has been significantly reduced and / or many new files with unlikely names (such as: yutuewyt.dll, 823746.dll, wuyetur.dll) have appeared. 
6) The antivirus is down: The antivirus will not start functioning as usual and you can not re-install it or install a different one. In some cases you can not even reach the website of the leading antivirus vendors. 
7) New Softwares: new softwares that you have never installed, appear on your desktop or on the tray bar. 

These symptoms, taken individually, do not give you the certainty of the presence of an e-virus in your PC, but they can instill you doubts. Of course, if the symptoms are more than one, the probability of being in presence of an e-virus increases.

More inside: E-Virus (Part II): Maybe your PC is infected by an e-virus... how to verify its presence?

Versione Italiana di questo articolo:
 "E-virus (parte I): Come riconoscere i sintomi di un E-INFLUENZA ovvero quando il nostro PC si รจ preso un E-VIRUS?"