Malware

Once malware is in your computer, it can wreak all sorts of havoc, from taking control of your machine, to monitoring your actions and keystrokes, to silently sending all sorts of confidential data from your computer or network to the attacker's home base

Cross-Site Scripting (XSS) 

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.

Un-patched software

The most common un-patched and exploited programs are browser add-in programs like Adobe Reader and other programs people often use to make surfing the web easier. It's been this way for many years now, but strangely, not a single company ever audited has ever had perfectly patched software. This is a gateway for malicious attacks.

SQL Injection Attack 

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. 

credential reuse

Once attackers have a collection of usernames and passwords from a breached website or service, 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.

An in-depth look at malicious attacks...

Phishing

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. In the email, there will be an attachment to open or a link to click

Man-in-the-Middle Attacks

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. 

Denial-of-Service (DoS) 

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. The server can't handle the massive amount of traffic, and as a result it gets so backed up that pretty much no one can leave.