Background on computer viruses

The only link we have was WiFi network and the PC's logged into chrome but not the laptop. I changed the desktop again and I ran a scan with Malware bites and Defender with zero results. It's as if their wallpaper jumped to each of my PC's in the network or logged in to the same account. Was this reply helpful? Yes No. Sorry this didn't help. Thanks for your feedback. Taking advantage of a flaw in the Microsoft Internet Information Server, the fast-replicating worm wreaked havoc by manipulating the protocols that allow computers to communicate and spread globally in just hours.

Eventually, as noted in Scientific American , compromised machines were used to launch a distributed denial of service attack on the Whitehouse. One of the most recent of the major viruses came out in , Heartbleed burst onto the scene and put servers across the Internet at risk. Heartbleed, unlike viruses or worms, stems from a vulnerability in OpenSSL, a general purpose, open source cryptographic library used by companies worldwide.

OpenSSL periodically sends out "heartbeats" to ensure that secure endpoints are still connected. Users can send OpenSSL a specific amount of data and then ask for the same amount back—for example, one byte.

If users claim they're sending the maximum allowed, 64 kilobytes, but only send a single byte, the server will respond with the last 64 kilobytes of data stored in RAM, notes security technologist, Bruce Schneier , which could include anything from user names to passwords to secure encryption keys.

For more than 60 years, computer viruses have been part of collective human consciousness, however what was once simply cyber vandalism has turned quickly to cybercrime.

Worms, Trojans and viruses are evolving. Hackers are motivated and clever, always willing push the boundaries of connection and code to devise new infection methods. The future of cybercrime seems to involve more PoS point of sale hacks, and, perhaps, the recent Moker remote access Trojan is a good example of what's to come. This newly-discovered malware is hard to detect, difficult to remove and bypasses all known defenses.

Nothing is certain—change is the lifeblood of both attack and defense. The general course goes something like this: the infected application executes usually at the request of the user , and the virus code is loaded into the CPU memory before any of the legitimate code executes.

At this point, the virus propagates itself by infecting other applications on the host computer, inserting its malicious code wherever it can. A resident virus does this to programs as they open, whereas a non-resident virus can infect executable files even if they aren't running. Boot sector viruses use a particularly pernicious technique at this stage: they place their code in the boot sector of the computer's system disk, ensuring that it will be executed even before the operating system fully loads, making it impossible to run the computer in a "clean" way.

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.

There are a couple other types you might want to be aware of:. Keep in mind that these category schemes are based on different aspects of a virus's behavior, and so a virus can fall into more than one category. A resident virus could also be polymorphic, for instance.