In today's threatscape, antivirus software provides little peace of mind. In fact, antimalware scanners on the whole are horrifically inaccurate, especially with exploits less than 24 hours old. After all, malicious hackers and malware can change their tactics at will. Swap a few bytes around, and a previously recognized malware program becomes unrecognizable.
To combat this, many antimalware programs monitor program behaviors, often called heuristics, to catch previously unrecognized malware. Other programs use virtualized environments, system monitoring, network traffic detection, and all of the above at once in order to be more accurate. And still they fail us on a regular basis.
Here are 11 sure signs you've been hacked and what to do in the event of compromise. Note that in all cases, the No. 1 recommendation is to completely restore your system to a known good state before proceeding. In the early days, this meant formatting the computer and restoring all programs and data. Today, depending on your operating system, it might simply mean clicking on a Restore button. Either way, a compromised computer can never be fully trusted again. The recovery steps listed in each category below are the recommendations to follow if you don't want to do a full restore -- but again, a full restore is always a better option, risk-wise.
Sure sign of system compromise No. 1: Fake antivirus messages
In slight decline these days, fake antivirus warning messages are among the surest signs that your system has been compromised. What most people don't realize is that by the time they see the fake antivirus warning, the damage has been done. Clicking No or Cancel to stop the fake virus scan is too little, too late. The malicious software has already made use of unpatched software, often the Java Runtime Environment or an Adobe product, to completely exploit your system.
Why does the malicious program bother with the "antivirus warning"? This is because the fake scan, which always finds tons of "viruses," is a lure to buy their product. Clicking on the provided link sends you to a professional-looking website, complete with glowing letters of recommendation. There, they ask you for your credit card number and billing information. You'd be surprised how many people get tricked into providing personal financial information. The bad guys gain complete control of your system and get your credit card or banking information. For bad guys, it's the Holy Grail of hacking.
What to do: As soon as you notice the fake antivirus warning message, power down your computer. (Note: This requires knowing what your legitimate antivirus program's warning looks like.) If you need to save anything and can do it, do so. But the sooner you power off your computer, the better. Boot up the computer system in Safe Mode, No Networking, and try to uninstall the newly installed software (oftentimes it can be uninstalled like a regular program). Either way, follow up by trying to restore your system to a state previous to the exploitation. If successful, test the computer in regular mode and make sure that the fake antivirus warnings are gone. Then follow up with a complete antivirus scan. Oftentimes, the scanner will find other sneak remnants left behind.
Sure sign of system compromise No. 2: Unwanted browser toolbars
This is probably the second most common sign of exploitation: Your browser has multiple new toolbars with names that seem to indicate the toolbar is supposed to help you. Unless you recognize the toolbar as coming from a very well-known vendor, it's time to dump the bogus toolbar.
What to do: Most browsers allow you to review installed and active toolbars. Remove any you didn't absolutely want to install. When in doubt, remove it. If the bogus toolbar isn't listed there or you can't easily remove it, see if your browser has an option to reset the browser back to its default settings. If this doesn't work, follow the instructions listed above for fake antivirus messages. You can usually avoid malicious toolbars by making sure that all your software is fully patched and by being on the lookout for free software that installs these tool bars. Hint: Read the licensing agreement. Toolbar installs are often pointed out in the licensing agreements that most people don't read.