Ransomware definitionRansomware is a form of malware that encrypts a victim's files. The attacker then demands a ransom from the victim to restore access to the data upon payment. Users are shown instructions for how to pay a fee to get the decryption key. The costs can range from a few hundred dollars to thousands, payable to cybercriminals in Bitcoin.How ransomware worksThere are a number of vectors ransomware can take to access a computer. One of the most common delivery systems is phishing spam — attachments that come to the victim in an email, masquerading as a file they should trust. Once they're downloaded and opened, they can take over the victim's computer, especially if they have built-in social engineering tools that trick users into allowing administrative access. Some other, more aggressive forms of ransomware, like NotPetya, exploit security holes to infect computers without needing to trick users.There are several things the malware might do once it’s taken over the victim's computer, but by far the most common action is to encrypt some or all of the user's files. If you want the technical details, the Infosec Institute has a great in-depth look at how several flavors of ransomware encrypt files. But the most important thing to know is that at the end of the process, the files cannot be decrypted without a mathematical key known only by the attacker. The user is presented with a message explaining that their files are now are now inaccessible and will only be decrypted if the victim sends an untraceable Bitcoin payment to the attacker.In some forms of malware, the attacker might claim to be a law enforcement agency shutting down the victim's computer due to the presence of pornography or pirated software on it, and demanding the payment of a "fine," perhaps to make victims less likely to report the attack to authorities. But most attacks don't bother with this pretense. There is also a variation, called leakware or doxware, in which the attacker threatens to publicize sensitive data on the victim's hard drive unless a ransom is paid. But because finding and extracting such information is a very tricky proposition for attackers, encryption ransomware is by far the most common type.Who is a target for ransomware?There are several different ways attackers choose the organizations they target with ransomware. Sometimes it's a matter of opportunity: for instance, attackers might target universities because they tend to have smaller security teams and a disparate user base that does a lot of file sharing, making it easier to penetrate their defenses.On the other hand, some organizations are tempting targets because they seem more likely to pay a ransom quickly. For instance, government agencies or medical facilities often need immediate access to their files. Law firms and other organizations with sensitive data may be willing to pay to keep news of a compromise quiet — and these organizations may be uniquely sensitive to leakware attacks.But don't feel like you're safe if you don't fit these categories: as we noted, some ransomware spreads automatically and indiscriminately across the internet.How to prevent ransomwareThere are a number of defensive steps you can take to prevent ransomware infection. These steps are a of course good security practices in general, so following them improves your defenses from all sorts of attacks:Keep your operating system patched and up-to-date to ensure you have fewer vulnerabilities to exploit.Don't install software or give it administrative privileges unless you know exactly what it is and what it does.Install antivirus software, which detects malicious programs like ransomware as they arrive, and whitelisting software, which prevents unauthorized applications from executing in the first place.And, of course, back up your files, frequently and automatically! That won't stop a malware attack, but it can make the damage caused by one much less significant.Ransomware removalIf your computer has been infected with ransomware, you'll need to regain control of your machine. CSO's Steve Ragan has a great video demonstrating how to do this on a Windows 10 machine:The video has all the details, but the important steps are to:Reboot Windows 10 to safe modeInstall antimalware softwareScan the system to find the ransomware programRestore the computer to a previous stateBut here's the important thing to keep in mind: while walking through these steps can remove the malware from your computer and restore it to your control, it won't decrypt your files. Their transformation into unreadability has already happened, and if the malware is at all sophisticated, it will be mathematically impossible for anyone to decrypt them without access to the key that the attacker holds. In fact, by removing the malware, you've precluded the possibility of restoring your files by paying the attackers the ransom they've asked for.Ransomware facts and figuresRansomware is big business. There's a lot of money in ransomware, and the market expanded rapidly from the beginning of the decade. In 2017, ransomware resulted in $5 billion in losses, both in terms of ransoms paid and spending and lost time in recovering from attacks. That's up 15 times from 2015. In the first quarter of 2018, just one kind of ransomware software, SamSam, collected a $1 million in ransom money.Some markets are particularly prone to ransomware—and to paying the ransom. Many high-profile ransomware attacks have occurred in hospitals or other medical organizations, which make tempting targets: attackers know that, with lives literally in the balance, these enterprises are more likely to simply pay a relatively low ransom to make a problem go away. It's estimated that 45 percent of ransomware attacks target healthcare orgs, and, conversely, that 85 percent of malware infections at healthcare orgs are ransomware. Another tempting industry? The financial services sector, which is, as Willie Sutton famously remarked, where the money is. It's estimated that 90 percent of financial institutions were targeted by a ransomware attack in 2017. Your anti-malware software won't necessarily protect you. Ransomware is constantly being written and tweaked by its developers, and so its signatures are often not caught by typical anti-virus programs. In fact, as many as 75 percent of companies that fall victim to ransomware were running up-to-date endpoint protection on the infected machines.Ransomware isn't as prevalent as it used to be. If you want a bit of good news, it's this: the number of ransomware attacks, after exploding in the mid '10s, has gone into a decline, though the initial numbers were high enough that it's still. But in the first quarter of 2017, ransomware attacks made up 60 percent of malware payloads; now it's down to 5 percent. Ransomware on the decline?What's behind this big dip? In many ways it's an economic decision based on the cybercriminal's currency of choice: bitcoin. Extracting a ransom from a victim has always been hit or miss; they might not decide to pay, or even if they want to, they might not be familiar enough with bitcoin to figure out how to actually do so.As Kaspersky points out, the decline in ransomware has been matched by a rise in so-called cryptomining malware, which infects the victim computer and uses its computing power to create (or mine, in cryptocurrency parlance) bitcoin without the owner knowing. This is a neat route to using someone else's resources to get bitcoin that bypasses most of the difficulties in scoring a ransom, and it has only gotten more attractive as a cyberattack as the price of bitcoin spiked in late 2017.That doesn't mean the threat is over, however. There are two different kinds of ransomware attackers: "commodity" attacks that try to infect computers indiscriminately by sheer volume and include so-called "ransomware as a service" platforms that criminals can rent; and targeted groups that focus on particularly vulnerable market segments and organizations. You should be on guard if you're in the latter category, no matter if the big ransomware boom has passed.With the price of bitcoin dropping over the course of 2018, the cost-benefit analysis for attackers might shift back. Ultimately, using ransomware or cryptomining malware is a business decision for attackers, says Steve Grobman, chief technology officer at McAfee. “As cryptocurrency prices drop, it’s natural to see a shift back [to ransomware]."Should you pay the ransom?If your system has been infected with malware, and you've lost vital data that you can't restore from backup, should you pay the ransom? When speaking theoretically, most law enforcement agencies urge you not to pay ransomware attackers, on the logic that doing so only encourages hackers to create more ransomware. That said, many organizations that find themselves afflicted by malware quickly stop thinking in terms of the "greater good" and start doing a cost-benefit analysis, weighing the price of the ransom against the value of the encrypted data. According to research from Trend Micro, while 66 percent of companies say they would never pay a ransom as a point of principle, in practice 65 percent actually do pay the ransom when they get hit.Ransomware attackers keep prices relatively low — usually between $700 and $1,300, an amount companies can usually afford to pay on short notice. Some particularly sophisticated malware will detect the country where the infected computer is running and adjust the ransom to match that nation's economy, demanding more from companies in rich countries and less from those in poor regions.There are often discounts offered for acting fast, so as to encourage victims to pay quickly before thinking too much about it. In general, the price point is set so that it's high enough to be worth the criminal's while, but low enough that it's often cheaper than what the victim would have to pay to restore their computer or reconstruct the lost data. With that in mind, some companies are beginning to build the potential need to pay ransom into their security plans: for instance, some large UK companies who are otherwise uninvolved with cryptocurrency are holding some Bitcoin in reserve specifically for ransom payments.There are a couple of tricky things to remember here, keeping in mind that the people you're dealing with are, of course, criminals. First, what looks like ransomware may not have actually encrypted your data at all; make sure you aren't dealing with so-called "scareware" before you send any money to anybody. And second, paying the attackers doesn't guarantee that you'll get your files back. Sometimes the criminals just take the money and run, and may not have even built decryption functionality into the malware. But any such malware will quickly get a reputation and won't generate revenue, so in most cases — Gary Sockrider, principal security technologist at Arbor Networks, estimates around 65 to 70 percent of the time — the crooks come through and your data is restored.Ransomware examplesWhile ransomware has technically been around since the '90s, it's only taken off in the past five years or so, largely because of the availability of untraceable payment methods like Bitcoin. Some of the worst offenders have been:CryptoLocker, a 2013 attack, launched the modern ransomware age and infected up to 500,000 machines at its height.TeslaCrypt targeted gaming files and saw constant improvement during its reign of terror.SimpleLocker was the first widespread ransomware attack that focused on mobile devicesWannaCry spread autonomously from computer to computer using EternalBlue, an exploit developed by the NSA and then stolen by hackers.NotPetya also used EternalBlue and may have been part of a Russian-directed cyberattack against Ukraine.Locky started spreading in 2016 and was "similar in its mode of attack to the notorious banking software Dridex." A variant, Osiris, was spread through phishing campaigns.Leatherlocker was first discovered in 2017 in two Android applications: Booster & Cleaner and Wallpaper Blur HD. Rather than encrypt files, it locks the home screen to prevent access to data.Wysiwye, also discovered in 2017, scans the web for open Remote Desktop Protocol (RDP) servers. It then tries to steal RDP credentials to spread across the network.Cerber proved very effective when it first appeared in 2016, netting attackers $200,000 in July of that year. It took advantage of a Microsoft vulnerability to infect networks.BadRabbit spread across media companies in Eastern Europe and Asia in 2017.SamSam has been around since 2015 and targeted primarily healthcare organizations.Ryuk first appeared in 2018 and is used in targeted attacks against vulnerable organizations such as hospitals. It is often used in combination with other malware like TrickBot.Maze is a relatively new ransomware group known for releasing stolen data to the public if the victim does not pay to decrypt it.RobbinHood is another EternalBlue variant that brought the city of Baltimore, Maryland, to its knees in 2019.GandCrab might be the most lucrative ransomware ever. Its developers, which sold the program to cybercriminals, claim more then $2 billion in victim payouts as of July 2019.Sodinokibi targets Microsoft Windows systems and encrypts all files except configuration files. It is related to GandCrabThanos is the newest ransomware on this list, discovered in January 2020. It is sold as ransomware as a service, It is the first to use the RIPlace technique, which can bypass most anti-ransomware methods. This list is just going to get longer. Follow the tips listed here to protect yourself.