After you open and run an infected program or attachment on your computer, you might not realize that you have introduced a virus until you notice something isn´t quite right.
Here are few primary indicators that your computer might be infected.
Your computer runs more slowly than normal
Your computer stops responding or locks up often
Your computer crashes and restarts every few minutes
Your computer restarts on its own and then fails to run normally
Applications on your computer don't work correctly
Disks or disk drives are inaccessible
You can't print correctly
You see unusual error messages
You see distorted menus and dialog boxes
These are common signs of infection—but they might also indicate hardware or software problems that have nothing to do with a virus. Unless you run the Microsoft Malicious Software Removal Tool and install industry-standard, up-to-date antivirus software on your computer, there is no way to be certain if your computer is infected with a virus or not.
Microsoft Security Essentials provides real-time protection for your home or small business PC that guards against viruses, spyware, and other malicious software.
Microsoft Security Essentials runs quietly and efficiently in the background so that you are free to use your Windows-based PC the way you want—without interruptions or long computer wait times.
Before installing Microsoft Security Essentials, we recommend that you uninstall other antivirus software already running on your PC. Running more than one antivirus program at the same time can potentially cause conflicts that affect PC
Tip: Beware of messages warning you that you sent e-mail that contained a virus. This can indicate that the virus has listed your e-mail address as the sender of tainted e-mail. This does not necessarily mean you have a virus. Some viruses have the ability to forge e-mail addresses.