You've got the latest, most up-to-date anti-virus software. You've run a full system scan and everything shows up "green" with no problems found. All appears to be running smoothly except that your web browser keeps redirecting you to casino websites regardless of what you type into Google. What the heck is going on?
It sounds like you might need a second opinion malware scanner to take a look at your system to see if your primary antivirus or anti-malware scanner might have let something slip onto your system undetected.
A second opinion scanner is just what it sounds like, a secondary malware detection and removal program that acts as a second line of defense for your computer should your primary scanner fail to detect an active malware infection
Most people think that a single scanner that has the latest virus / malware definitions will protect their system from harm, unfortunately, this is not always the case. Virus and malware developers are deliberately coding their malware to evade detection by many of the major virus / malware scanners on the market. The bad guys use encryption, stealth techniques, and all manners of black art coding to hide their payloads, which are usually malicious software packages designed to enslave your computer while making the developers and their malware affiliates money.
Why does a second opinion scanner find things that your primary scanner doesn't?
There are several factors that affect malware detection. Different malware scanners may use different methods of scanning. One may specialize in rootkit detection while another may only be looking for specific virus signatures.
I have personally witnessed an infestation of a rootkit that managed to evade detection by four of the leading antivirus / anti-malware scanners on the market today. Rootkits are especially hard to detect because they can be installed in firmware or low-level drivers that some scanning tools can't inspect at all.
There are many varieties of second opinion scanners available today but you need to be very careful when selecting one because some malware developers will produce fake anti-virus products or Scareware that will actually introduce malware into your system rather than removing it. Many of them have very smart sounding names and may have very convincing websites that appear to be legit. You should Google any scanner you are thinking of using to make sure it is legit and not a scam.
Here is a list of some of the more reputable, legitimate, and effective second opinion scanners on the market:
Malwarebytes (Windows) - One of the most widely recommended second opinion scanners on the market. It is updated very frequently and has the ability to detect many forms of malware that traditional virus scanners miss. There is a free version available as well as a paid version that offers real-time protection.
HitMan Pro (Windows) - HitMan Pro takes a unique cloud-based approach to malware scanning. It can scan a computer for many forms of malware in a very short amount of time. It also has a free version available.
Kaspersky TDS Killer Anti-rootkit Utility (Windows) - The TDS Killer scanner is one of my favorite tools of last resort. If you think you have a rootkit on your system that has been missed by all other tools, TDS Killer is often your last and best hope of eradicating the rootkit. It is a free tool that focuses on the TDL variety of root kits that are very sophisticated and extremely difficult to detect and remove.
Even if the second opinion scanner you installed fails to discover the malware that you are confident is still hiding on your system, all hope is not lost. There is an excellent website called Bleeping Computer that has a knowledgeable staff of expert volunteers who will guide you through the process of finding and ridding your computer of just about any form of malware that exists today. They have a diagnostic process that requires some effort on your part, but they are there to help you every step of the way.