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Symptoms of a Virus Infected Computer
Part I
Symptoms may not be malware-related
The examples listed below are common symptoms of malware, but your computer may  exhibit many of these symptoms for legitimate reasons unrelated to malware, such as software or hardware incompatibilities or system instability.
Symptom of malware affecting currently installed Internet Security System (Antivirus+) products:

  • Your Antivirus product is disabled for no reason and cannot be restarted
  • A threat is discovered or the Threat Detected window keeps appearing
  • You receive frequent alerts from your ISS Personal firewall about an unknown program
  • You receive pop-up alerts from rogue antivirus programs1 claiming that you are infected with multiple viruses
Symptoms of computer malware that affect the Internet:
  • You may receive the error "Internet Explorer could not display the page" when attempting to access certain websites
  • Your web browser (for example, Microsoft Internet Explorer, Mozilla Firefox, Google Chrome) freezes, hangs or is unresponsive
  • Your web browser's default home page is changed
  • Access to your ISS web page is blocked
  • You get redirected to web pages other than the one you intended to go to
  • You receive numerous web-browser pop-up messages
  • Strange or unexpected toolbars appear at the top of your web browser

Malware symptoms that affect system performance:
  • Your computer runs slower than usual
  • Your computer freezes, hangs or is unresponsive
  • There are new icons on your Desktop that you do not recognize
  • Your computer restarts by itself (but not a restart caused by Windows Updates
  • You see unusual error messages (for example, messages saying there are missing or corrupt files folders)
  • You are unable to access the Control Panel, Task Manager, Registry Editor or Command Prompt

Symptoms of malware in email:
  • You receive messages in your mailbox without a sender address or subject
  • People receive spam email from your email address with a third-party email program installed (for example, Microsoft Outlook, Outlook Express/Windows Mail, Windows Live Mail and Mozilla Thunderbird)

See "How to recognize and prevent spam mail" coming soon ....

1 What Is Rogue Antivirus?

Rogue antivirus is a loose family of programs that claim to scan a computer for malware and then display fake warnings indicating that the system has been severely compromised.  These alarming messages are an attempt to frighten and trick the recipient into entering their credit card number into a web site in order to "purchase" a full version of the software which will remove the "threats" it detected.

While it is common for legitimate antivirus vendors to provide free trial versions, all reputable vendors offer some form of free removal capability or support before asking for a credit card, since the foundation of building a good relationship with a new customer is based on trust, rather than scaring them.
Rogue antivirus programs can reach a computer in various ways:  Spam messages that contain a link or an attached file and malicious web sites that have been optimized to appear first in search results through black hat SEO (see below) search engine optimization are two popular techniques.  They are also regularly spread through bots, Trojans and other forms of malware to make commissions through criminal affiliate sales networks.  The means of distribution vary quite widely, as do the names displayed by and symptoms of these fraudulent virus fighting programs.

What is Black Hat SEO?

Black Hat SEO refers to a set of practices that are used to increase a site or page's rank in search engines through means that violate the search engines' terms of service.  The term "black hat" originated in Western movies to distinguish the "bad guys" from the "good guys," who wore white hats.  Recently, it's used more commonly to describe computer hackers, virus creators, and those who perform unethical actions with computers.