SQL (pronounced “sequel”) stands for structured query language; it’s a programming language used to communicate with databases. Many of the servers that store critical data for websites and services use SQL to manage the data in their databases. A SQL injection attack specifically targets this kind of server, using malicious code to get the server to divulge information it normally wouldn’t. This is especially problematic if the server stores private customer information from the website, such as credit card numbers, usernames and passwords (credentials), or other personally identifiable information, which are tempting and lucrative targets for an attacker. An SQL injection attack works by exploiting any one of the known SQL vulnerabilities that allow the SQL server to run malicious code. For example, if a SQL server is vulnerable to an injection attack, it may be possible for an attacker to go to a website’s search box and type in code that would force the site’s SQL server to dump all of its stored usernames and passwords for the site.

Imagine you’re sitting in traffic on a one-lane country road, with cars backed up as far as the eye can see. Normally this road never sees more than a car or two, but a county fair and a major sporting event have ended around the same time, and this road is the only way for visitors to leave town. The road can’t handle the massive amount of traffic, and as a result it gets so backed up that pretty much no one can leave. That’s essentially what happens to a website during a denial of service (DoS) attack. If you flood a website with more traffic than it was built to handle, you’ll overload the website’s server and it’ll be nigh-impossible for the website to serve up its content to visitors who are trying to access it. This can happen for innocuous reasons of course, say if a massive news story breaks and a newspaper’s website gets overloaded with traffic from people trying to find out more. But often, this kind of traffic overload is malicious, as an attacker floods a website with an overwhelming amount of traffic to essentially shut it down for all users. In some instances, these DoS attacks are performed by many computers at the same time. This scenario of attack is known as a Distributed Denial of Service Attack (DDoS). This type of attack can be even more difficult to overcome due to the attacker appearing from many different IP addresses around the world simultaneously, making determining the source of the attack even more difficult for network administrators.

Users today have so many logins and passwords to remember that it’s tempting to reuse credentials here or there to make life a little easier. Even though security best practices universally recommend that you have unique passwords for all your applications and websites, many people still reuse their passwords—a fact attackers rely on. Once attackers have a collection of usernames and passwords from a breached website or service (easily acquired on any number of black market websites on the internet), they know that if they use these same credentials on other websites there’s a chance they’ll be able to log in. No matter how tempting it may be to reuse credentials for your email, bank account, and your favorite sports forum, it’s possible that one day the forum will get hacked, giving an attacker easy access to your email and bank account. When it comes to credentials, variety is essential. Password managers are available and can be helpful when it comes to managing the various credentials you use.

When an attacker wants you to install malware or divulge sensitive information, they often turn to phishing tactics, or pretending to be someone or something else to get you to take an action you normally wouldn’t. In a phishing attack, an attacker may send you an email that appears to be from someone you trust, like your boss or a company you do business with. The email will seem legitimate, and it will have some urgency to it (e.g. fraudulent activity has been detected on your account). In the email, there will be an attachment to open or a link to click. Upon opening the malicious attachment, you’ll thereby install malware in your computer. If you click the link, it may send you to a legitimate-looking website that asks for you to log in to access an important file—except the website is actually a trap used to capture your credentials when you try to log in.

In an SQL injection attack, an attacker goes after a vulnerable website to target its stored data, such as user credentials or sensitive financial data. But if the attacker would rather directly target a website’s users, they may opt for a cross-site scripting attack. Similar to an SQL injection attack, this attack also involves injecting malicious code into a website, but in this case the website itself is not being attacked. Instead, the malicious code the attacker has injected only runs in the user’s browser when they visit the attacked website, and it goes after the visitor directly, not the website. One of the most common ways an attacker can deploy a cross-site scripting attack is by injecting malicious code into a comment or a script that could automatically run. For example, they could embed a link to a malicious JavaScript in a comment on a blog. Cross-site scripting attacks can significantly damage a website’s reputation by placing the users’ information at risk without any indication that anything malicious even occurred. Any sensitive information a user sends to the site—such as their credentials, credit card information, or other private data—can be hijacked via cross-site scripting without the website owners realizing there was even a problem in the first place.

When you’re on the internet, your computer has a lot of small back-and-forth transactions with servers around the world letting them know who you are and requesting specific websites or services. In return, if everything goes as it should, the web servers should respond to your request by giving you the information you’re accessing. This process, or session, happens whether you are simply browsing or when you are logging into a website with your username and password. The session between your computer and the remote web server is given a unique session ID, which should stay private between the two parties; however, an attacker can hijack the session by capturing the session ID and posing as the computer making a request, allowing them to log in as an unsuspecting user and gain access to unauthorized information on the web server. There are a number of methods an attacker can use to steal the session ID, such as a cross-site scripting attack used to hijack session IDs. An attacker can also opt to hijack the session to insert themselves between the requesting computer and the remote server, pretending to be the other party in the session. This allows them to intercept information in both directions and is commonly called a man-in-the-middle attack.