If the compromised logon information is used on other websites, immediately change those passwords. And be more careful next time. Websites rarely send emails asking you to provide your logon information. When in doubt, go to the website directly (don't use the links sent to you in email) and see if the same information is being requested when you log on using the legitimate method. You can also call the service via their phone line or email them to report the received phish email or to confirm its validity. Lastly, consider using online services that provide two-factor authentication. It makes your account much harder to steal.
Sure sign of system compromise No. 7: Unexpected software installs
Unwanted and unexpected software installs are a big sign that your computer system has likely been hacked.
In the early days of malware, most programs were computer viruses, which work by modifying other legitimate programs. They did this to better hide themselves. For whatever reason, most malware programs these days are Trojans and worms, and they typically install themselves like legitimate programs. This may be because their creators are trying to walk a very thin line when the courts catch up to them. They can attempt to say something like, "But we are a legitimate software company." Oftentimes the unwanted software is legally installed by other programs, so read your license agreements. Frequently, I'll read license agreements that plainly state that they will be installing one or more other programs. Sometimes you can opt out of these other installed programs; other times you can't.
What to do: There are many free programs that show you all your installed programs and let you selectively disable them. My favorite for Windows is Autoruns. It doesn't show you every program installed but will tell you the ones that automatically start themselves when your PC is restarted. Most malware programs can be found here. The hard part is determining what is and what isn't legitimate. When in doubt, disable the unrecognized program, reboot the PC, and reenable the program only if some needed functionality is no longer working.
Sure sign of system compromise No. 8: Your mouse moves between programs and makes correct selections
If your mouse pointer moves itself while making selections that work, you've definitely been hacked. Mouse pointers often move randomly, usually due to hardware problems. But if the movements involve making the correct choices to run particular programs, malicious humans are somewhere involved.
Not as common as some of the other attacks, many hackers will break into a computer, wait for it to be idle for a long time (like after midnight), then try to steal your money. Hackers will break into bank accounts and transfer money, trade your stocks, and do all sorts of rogue actions, all designed to lighten your cash load.
Sign up for CIO Asia eNewsletters.