Ways computer viruses spread

Once the virus has its hooks into your computer, it can start executing its payload, which is the term for the part of the virus code that does the dirty work its creators built it for.

These can include all sorts of nasty things: Viruses can scan your computer hard drive for banking credentials, log your keystrokes to steal passwords, turn your computer into a zombie that launches a DDoS attack against the hacker's enemies, or even encrypt your data and demand a bitcoin ransom to restore access. Other types of malware can have similar payloads, of course: there are ransomware worms and DDoS Trojans and so forth.

In the early, pre-internet days, viruses often spread from computer to computer via infected floppy disks. The SCA virus, for instance, spread amongst Amiga users on disks with pirated software. Today, viruses spread via the internet. In most cases, applications that have been infected by virus code are transferred from computer to computer just like any other application. Because many viruses include a logic bomb — code that ensures that the virus's payload only executes at a specific time or under certain conditions — users or admins may be unaware that their applications are infected and will transfer or install them with impunity.

Infected applications might be emailed inadvertently or deliberately — some viruses actually hijack a computer's mail software to email out copies of themselves ; they could also be downloaded from an infected code repository or compromised app store. One thing you'll notice that all of these infection vectors have in common is that they require the victim to execute the infected application or code. Remember, a virus can only execute and reproduce if its host application is running!

Still, with email such a common malware dispersal method, a question that causes many people anxiety is: Can I get a virus from opening an email?

The answer is that you almost certainly can't simply by opening a message; you have to download and execute an attachment that's been infected with virus code. That's why most security pros are so insistent that you be very careful about executing email attachments, and why most email clients and webmail services include virus scanning features by default. A particularly sneaky way that a virus can infect a computer is if the infected code runs as JavaScript inside a web browser and manages to exploit security holes to infect programs installed locally.

Some email clients will execute HTML and JavaScript code embedded in email messages, so strictly speaking, opening such messages could infect your computer with a virus. But most email clients and webmail services have built-in security features that would prevent this from happening, so this isn't an infection vector that should be one of your primary fears. Symantec has a good breakdown on the various types of viruses you might encounter , categorized in different ways.

We've already met resident and non-resident viruses , boot sector viruses , web scripting viruses , and so on.

Author AllBusiness. More from AllBusiness. Yahoo Small Business. In the game, computer programs vie for control of a virtual computer. The game was essentially a battle arena where computer programmers could pit their viral creations against each other. For two dollars Dewdney would send detailed instructions for setting up your own Core War battles within the confines of a virtual computer.

What would happen if a battle program was taken out of the virtual computer and placed on a real computer system? In a follow-up article for Scientific American, Dewdney shared a letter from two Italian readers who were inspired by their experience with Core War to create a real virus on the Apple II. The brainchild of Pakistani brothers and software engineers, Basit and Amjad Farooq, Brain acted like an early form of copyright protection, stopping people from pirating their heart monitoring software.

Other than guilt tripping victims in to paying for their pirated software, Brain had no harmful effects. BHP also has the distinction of being the first stealth virus; that is, a virus that avoids detection by hiding the changes it makes to a target system and its files. The cover image depicted viruses as cute, googly eyed cartoon insects crawling all over a desktop computer.

Up to this point, computer viruses were relatively harmless. Yes, they were annoying, but not destructive. So how did computer viruses go from nuisance threat to system destroying plague? The MacMag virus caused infected Macs to display an onscreen message on March 2, The infected Freehand was then copied and shipped to several thousand customers, making MacMag the first virus spread via legitimate commercial software product.

The Morris worm knocked out more than 6, computers as it spread across the ARPANET , a government operated early version of the Internet restricted to schools and military installations. The Morris worm was the first known use of a dictionary attack. As the name suggests, a dictionary attack involves taking a list of words and using it to try and guess the username and password combination of a target system.

Robert Morris was the first person charged under the newly enacted Computer Fraud and Abuse Act , which made it illegal to mess with government and financial systems, and any computer that contributes to US commerce and communications.

In his defense, Morris never intended his namesake worm to cause so much damage. According to Morris, the worm was designed to test security flaws and estimate the size of the early Internet. A bug caused the worm to infect targeted systems over and over again, with each subsequent infection consuming processing power until the system crashed.

Victims received a 5. Joseph L. Popp, intended to draw parallels between his digital creation and the deadly AIDS virus. In an era before Bitcoin and other untraceable cryptocurrencies, victims had to send ransom funds to a PO box in Panama in order to receive the decryption software and regain access to their files. There were 2. By the end of the decade, that number would surpass million.

Traditional AV works by comparing the files on your computer with a giant list of known viruses. Every virus on the list is made of computer code and every snippet of code has a unique signature—like a fingerprint. If a snippet of code found on your computer matches that of a known virus in the database, the file is flagged.

While each copy of the virus looked and acted the same, the underlying code was different. This is called polymorphic code, making the first polymorphic virus. Melissa was a macro virus. Viruses of this type hide within the macro language commonly used in Microsoft Office files. Opening up a viral Word doc, Excel spreadsheet, etc. Comodo Antivirus will automatically contain unknown virus files. It will efficiently block hackers from stealing your valuable data or damaging your computer!

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