In January 1986, two brothers from Pakistan wrote some code and created something that would impact home computing three decades later – the first computer virus.

Amjad Farooq Alvi and Basit Farooq Alvi ran Brain Computer Services. It’s thought they created the virus to protect their software from being pirated.

Dubbed ‘Brain’ it as a boot sector virus targeting MS-DOS computers, it infected the boot sector but didn’t cause severe damage.

Viruses are just one of a host of threats a computer has to deal with when it’s connected to the internet, but there are at least some effective countermeasures. Perhaps the most important of these are common sense and a basic understanding of how computer viruses work.

A brief history

A computer virus is the electronic equivalent of the viruses that cause illnesses in people — and they cause all manner of ailments, too.

Computer viruses are just one type of ‘malware’ — software written solely to cause problems for the unlucky victim.

The first examples appeared in the 1970s, but they were more experiments than deliberate attempts to wreak havoc.

The PC boom of the late 1980s saw viruses really take off and most were spread via floppy disks. When an ‘infected’ disk was used, the virus copied itself onto the PC, where it could then infect other floppy disks.

Floppy disk viruses tended to just delete files and display on-screen messages, but their reliance on passing disks around to spread meant few could really run wild. This all changed, however, with the rise of the internet.

The worm returns

Those early viruses of the 1970s were technically ‘worms’, because they spread over computer networks, rather than by infecting software stored on a disk. Since the internet is essentially a vast network that connects computers all over the world, it’s little surprise that worms returned as internet access grew in the 1990s.

Trojan software virus

The most successful worms were spread by email. When someone opens an infected message attachment that appears to be from a known contact — usually sent with an enticing subject line — the worm was activated and went on to propagate by emailing itself to everyone in that person’s email address book.

Trojan software

The internet’s usefulness for distributing software easily soon led to a third kind of malware — the trojan. Named after the Trojan horse from Greek mythology, trojans are malware that masquerade as normal software.

Trojans are rife on file-sharing networks, but hacked websites can also deliver trojans via security holes in a web browser — known as a ‘drive-by download’. That’s one reason why it’s essential to  use the latest version of a web browser, since most browser updates are made to close such security holes.

Windows 7 IE 11

Microsoft recently ended support for Internet Explorer 8,9 and 10, leaving Windows XP users vulnerable. Find out more in our article: What the end of Internet Explorer means for you.

Trojans can cause serious harm on a PC by encrypting its files and demanding a ransom to decrypt them. Some, however, are more insidious and turn a PC into a ‘zombie’.

Hackers can control zombie PCs remotely without the owner’s knowledge. Most are used to send spam and launch ‘DDoS’ (Distributed Denial of Service) attacks on business websites, but hackers can also harvest personal and financial information to sell to criminal organisations.

Who’s at risk?

Anyone who uses a computer connected to the internet is at risk from malware and viruses of all kinds, but some computers are more at risk than others.

Since it’s the most popular operating system around the world, considerably more malware is aimed at Microsoft Windows than any other. That means every Windows user should be using anti-malware software of some description, both to prevent potential malware attacks and detect existing infections. BT offers customers BT Virus Protect (see below).

Check out our article: What to do if your computer is affected by malware.

Preventing infection

For Windows users, the best defence against viruses and other malware is a good anti-virus program. Microsoft Security Essentials a free download that should beinstalled on any Windows 7 PC, while Windows 8.1 and 10 include Windows Defender for a similar level of security.

Use BT’s free anti-virus software

BT broadband customers can protect their devices against computer virus protection for free, with BT Virus Protect.

Developed in conjunction with McAfee, it’s packed with features to protect your computer against online threats including: VirusScan, Personal Firewall, Parental controls and SiteAdvisor. Read more.

Depending on your broadband package, you either get a two- or 15-licence and you can upgrade to a 15-licence for £4 a month.

Virus Protect is easy to install. Log into the My BT website, scroll down to My Extras, look for Virus Protect and click Get Started to begin the download.

Keep your browser up to date

As already mentioned, using the latest version of your favourite web browser is also strongly recommended, as is keeping Windows up-to-date with Windows Update.

Free software scam

It’s also advisable to download software only from trusted sources (usually the manufacturer’s website) and avoid online offers that look to good to be true. A free version of Microsoft Office, for example, is likely to be anything but.

Read more: 10 ways BT's free software keeps you safe online

BT Extras