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.
Sure sign of system compromise No. 3: Redirected Internet searches
Many hackers make their living by redirecting your browser somewhere other than you want to go. The hacker gets paid by getting your clicks to appear on someone else's website, often those who don't know that the clicks to their site are from malicious redirection.
You can often spot this type of malware by typing a few related, very common words (for example, "puppy" or "goldfish") into Internet search engines and checking to see whether the same websites appear in the results -- almost always with no actual relevance to your terms. Unfortunately, many of today's redirected Internet searches are well hidden from the user through use of additional proxies, so the bogus results are never returned to alert the user. In general, if you have bogus toolbar programs, you're also being redirected. Technical users who really want to confirm can sniff their own browser or network traffic. The traffic sent and returned will always be distinctly different on a compromised computer vs. an uncompromised computer.
What to do: Follow the same instructions as above. Usually removing the bogus toolbars and programs is enough to get rid of malicious redirection.
Sure sign of system compromise No. 4: Frequent random popups
This popular sign that you've been hacked is also one of the more annoying ones. When you're getting random browser pop-ups from websites that don't normally generate them, your system has been compromised. I'm constantly amazed about which websites, legitimate and otherwise, can bypass your browser's anti-pop-up mechanisms. It's like battling email spam, but worse.
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