Hacking includes a wide range of activities, but these generally can be divided into two categories:

Below we outline 6 signs in both categories that will let you know you have been hacked and how to act if your device is intruded upon.

In all cases, the recommendation to be made in a timely manner is to restore the system to its pre-intrusion state before proceeding with the recovery phase (this means formatting the computer and restoring all programs and data). However, a hacked computer can never be completely secure again.

This is the heyday of ransomware (such as the infamous Cryptolocker), which is malware (malicious software) created to disrupt a computer's activities, steal sensitive information, or display unwanted advertisements in order to obtain a ransom in exchange for decrypting them. If you are lucky, some of the ransomware messages come from programs that do not block your data (known as scareware) and as a result, restarting your computer is enough to make it disappear.

If, however, after rebooting, the same ransomware screen returns or you are unable to access your data, there are some actions you can take: restore your data if it has been backed up previously; access sites that could help you recover your files without paying the ransom due to their ability to figure out the shared secret encryption key or another way to decrypt the ransomware program.

However, security experts will advise you never to pay the ransom, first of all because it is illegal, and secondly, you could be prosecuted as a flanker.

In recent times they have been seen less but never go out of fashion: false antivirus warning messages (other than the antivirus program you are using)-considered among the surest signs that your system has been attacked.

Once the message is displayed, the damage is done and consequently it is too late to take action on the intrusion. How does it work? The fake scan, which always uncovers tons of "viruses," is a bait to get you to buy their product.

By clicking on the link provided, you land on a website (which appears to be secure) where you are asked for your credit card number and billing information, and your payment goes straight into the hackers' pockets.

What to do. As soon as you notice the fake message, shut down the computer or boot the computer system in safe mode, without a network, and try uninstalling the newly installed software (it can often be uninstalled like a normal program). In either case, you should try to restore the system to a state prior to the intrusion. If successful, test the computer in normal mode and make sure the false antivirus alerts are gone.

After that, run a full antivirus scan, which often finds other unwanted components left behind.

This is a very common sign of misuse of one's computer.

Most browsers (from Google, to FireFox) allow you to review installed and active toolbars, so simply remove those that were not installed voluntarily and in any case remove even those you are unsure of.

If the counterfeit toolbar is not listed or you cannot easily remove it, you need to check if your browser has a restore option on default settings. If that doesn't work either, you need to follow the instructions for fake antivirus messages

Many hackers make a living by redirecting your browser to a link other than the one you want. Unfortunately, to date many of the redirected Internet searches are well hidden from the user through the use of additional proxies, so the bogus results are never returned to alert the user.

This breach signal is one of the most annoying. When you receive random browser popups from Web sites that do not normally generate them, it means that your system has been compromised. Usually random popups are generated by one of the previous signals above. For example, you have to get rid of fake toolbars or other programs to stop displaying the malicious popups.

Sometimes it can happen that you receive friend requests on social media when you are already connected with that person.

Immediately you think that the request was not accepted so it was resent; after that you notice that person's profile is devoid of recognizable friends and has none of the older posts.

Or the same issue happens in reverse (i.e. you are sending new requests). In either case, the hacker checks your social profile and has created a second, similar bogus page, or you or a friend has installed a bogus social media application.

In this case, your first action is to warn your mutual friends not to accept the application. Finally, contact the site to report the incident and change your authentication method.