What usually happens in this scenario is that the victim responded to an authentic-looking phishing email that purportedly claimed to be from the service. The bad guy uses it to collect the logon information, logs on, changes the password (and other information to complicate recovery), and uses the service to steal money from the victim or the victim's acquaintances (while pretending to be the victim).
What to do: If the scam is widespread and many of your acquaintances have been contacted, immediately notify all your close contacts about your compromised account. This will minimize the damage being done to others by your mistake. Second, contact the online service to report the compromised account. Most online services now have easy methods or email contact addresses to report compromised accounts. If you report your account as compromised, usually the service will do the rest to help you restore your legitimate access. Also, consider enacting MFA.
If the compromised logon information is used on other websites, immediately change those passwords. 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 its phone line or email them to report the received phish email or to confirm its validity.
8. You observe unexpected software installs
Unwanted and unexpected software installs are a big sign that your computer has 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. 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."
The unwanted software is often 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; sometimes you can't.
What to do: There are many programs that will show you all your installed programs and let you selectively disable them. My favorite checkers for Microsoft Windows are Microsoft’s free programs, Autoruns or Process Explorer. They don't show you every program installed but they will tell you the ones that automatically start themselves when your PC is restarted (Autoruns) or the ones currently running (Process Explorer).
Most malware programs will be found embedded in the much larger list of legitimate running programs. The hard part can be determining what is and what isn't legitimate. You can enable the “Check VirusTotal.com” options, and the programs, along with Google’s Virustotal.com web site, will tell you which ones it thinks are malware. When in doubt, disable the unrecognized program, reboot the PC, and re-enable the program only if some needed functionality is no longer working.
9. Your mouse moves between programs and makes selections
If your mouse pointer moves itself while making selections that work (this is the important part), you've definitely been hacked. Mouse pointers often move randomly, usually due to hardware problems. If the movements involve making choices to run particular programs, malicious humans are somewhere involved.
This technique is not as common as some other attacks. 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.
What to do: If your computer "comes alive" one night, take a minute before turning it off to determine what the intruders are interested in. Don't let them rob you, but it will be useful to see what they are looking at and trying to compromise. Take a few pictures to document their tasks. When it makes sense, power off the computer. Unhook it from the network (or disable the wireless router) and call in the professionals. This is the one time that you're going to need expert help.
Using another known good computer, immediately change all your other logon names and passwords. Check your bank account transaction histories, stock accounts and so on. Consider paying for a credit-monitoring service. If you've been a victim of this attack, you have to take it seriously. Complete restore of the computer is the only option you should choose for recovery. If you've lost any money, make sure to let the forensics team make a copy first. If you've suffered a loss, call law enforcement and file a case. You'll need this information to best recover your real money losses, if any.
10. Antimalware, Task Manager or Registry Editor is disabled
This is a huge sign of malicious compromise. If you notice that your antivirus software is disabled and you didn't do it, you're probably exploited — especially if you try to start Task Manager or Registry Editor and they won't start, start and disappear, or start in a reduced state.
What to do: Perform a complete restore because there is no telling what has happened. If you want to try something less drastic first, if on a Windows computer, try running Microsoft Autoruns or Process Explorer (or similar programs) root out the malicious program causing the problems. They will usually identify your problem program, which you can then uninstall or delete.
If the malware “fights back” and won’t let you easily uninstall it, research the many methods on how to restore the lost functionality (any internet search engine will return lots of results), then restart your computer in Safe Mode and start the hard work. I say "hard work" because usually it isn't easy or quick. Often, I have to try a handful of different methods to find one that works. Precede restoring your software by getting rid of the malware program using the methods listed above.
11. Your online account is missing money
I mean lots of money. Online bad guys don't usually steal a little money. They like to transfer everything or nearly everything, often to a foreign exchange or bank. Usually it begins by your computer being compromised or from you responding to a fake phish from your bank or stock trading company. The bad guys log on to your account, change your contact information, and transfer large sums of money to themselves.
What to do: In most cases you are in luck because most financial institutions will replace the stolen funds (especially if they can stop the transaction before the damage is truly done). However, there have been cases where the courts have ruled it was the customer's responsibility not to be hacked, and it's up to the financial institution to decide whether they will make restitution to you.
To prevent this from happening in the first place, turn on transaction alerts that send text alerts to you when something unusual is happening. Many financial institutions allow you to set thresholds on transaction amounts, and if the threshold is exceeded or it goes to a foreign country, you'll be warned. Unfortunately, many times the bad guys reset the alerts or your contact information before they steal your money. So, make sure your financial or trading institution sends you alerts anytime your contact information or alerting choices are changed.
12. You’ve been notified by someone you’ve been hacked
One of the top ways that any organization finds out they have been successfully compromised is notification by an unrelated third party. This has been the case since the beginning of computers and continues to be true. Verizon’s respected Data Breach Investigations Report has revealed that more companies were notified that they were hacked by unrelated third parties than organizations that recognized their own compromises. In July 2019, Microsoft revealed that it had detected nation-state attacks against over 10,000 of its customers since the beginning of the year.
What to do: First, figure out if you have truly been hacked. Make sure everyone slows down until you confirm that you have been successfully compromised. If confirmed, follow your predefined incident response plan. You have one, right? If not, make one now and practice with stakeholders. Make sure that everyone knows that your IR plan is a thoughtful plan that must be followed. You don’t want anyone going off on their own hunting parties or anyone inviting more people “to the party” before it’s decided who needs to be involved. Your biggest challenge is going to be actually having people follow the plan in an emergency. Communicate and practice, ahead of time.
13. Confidential data has been leaked
Nothing confirms you’ve been hacked like your organization’s confidential data sitting out on the internet or dark web. If you didn’t notice it first, then likely the media and other interested stakeholders will be contacting your organization to confirm or find out what you are doing about it.
What to do: Like the previous sign, first find out if it’s true that it is really your confidential data out there. In more than a few cases, hackers have claimed to compromise a company’s data but didn’t have anything confidential. Either they made up the claim and data, only had publicly available data, or they had some other company’s data. So, first confirm.
If it is your organization’s confidential data, it’s time to tell senior management, begin the IR process, and figure out what needs to be communicated to whom by when. In many countries and states, the legal requirement to report compromised customer data can be as short as 72 hours, and many times you won’t even be able to confirm the leak or how it happened in 72 hours. It goes without saying that you need to get legal involved.
14. Your credentials are in a password dump
Literally billions of valid (at least at one time) logon credentials are on the internet and dark web. They have usually been compromised by phishing, malware or website database breaches. You will not usually be notified by third parties as is the case with other types of data leaks. You have to proactively look out for this sort of threat. The sooner you know this sort of thing has happened the better.
You can check for compromised credentials one at a time using various websites (like Have I Been Pwned), check across multiple accounts using various free open source intelligence tools (like The Harvester), free commercial tools (like KnowBe4’s Password Exposure Test), or any of the commercial services that look for your company’s data and credentials all the time for a fee.
What to do: After first confirming whether the dump contains any currently used credentials, reset all your logon credentials. Start an IR process to see if you can figure out how your organization’s logon credentials ended up outside the company. Also, implement MFA.
15. You observe strange network traffic patterns
Many a compromise was first noticed by strange, unexpected network traffic patterns. It could have been a bad distributed denial of service (DDoS) attack against your company’s web servers or large, expected file transfers to sites in countries you do not do business with. If more companies understood their legitimate network traffic patterns there would less need for a third party to tell them they are compromised. It’s good know that most of the servers in your company don’t talk to other servers in your company. Most servers in your company don’t talk to every workstation in your company and vice-versa. Most workstations in your company should not be using non-HTTP/non-HTTPS protocols to talk directly to other places on the internet.
What to do: If you see unexpected, strange traffic that you cannot explain, it’s probably best to kill the network connection and start an IR investigation. Years ago, we probably would have said to err on the side of operational caution. Today, you can’t take any chances. Kill any suspicious transfers until they are proven legitimate.
If you don’t understand your valid network traffic, you need to do so. Dozens of tools are designed to help you better understand and document your network traffic. I would recommend checking out the free, open-source alternatives like Bro and Snort, but both require a lot of time, resources and research to use effectively. Instead, find a good commercial solution that has already done all the hard work for you.
Prevention is the best cure
The hope that an antimalware program can perfectly detect malware and malicious hacking is pure folly. Keep an eye out for these common signs and symptoms of your computer being hacked. If you are risk-adverse, as I am, always perform a complete computer restore with the event of a breach. Once your computer has been compromised, the bad guys can do anything and hide anywhere. It's best to just start from scratch.
Most malicious hacking originates from one of three vectors: running Trojan horse programs, unpatched software, and responding to fake phishing emails. Do better at preventing these three things, and you'll be less likely to have to rely on your antimalware software's accuracy -- and luck.