A macro virus is essentially a virus written in the same language used to develop software applications, such as Microsoft Word and Microsoft Excel. These applications contain very powerful macro languages which can be used to automate tasks and create tabs and forms. These macros can run automatically in the form of scripts, so that routine tasks are completed when a file is opened.
The first macro virus surfaced around 1995 and infected Microsoft Word, known as Concept. Another type of macro virus originated in 1999, known as Melissa. Opening the attachment in the email caused the email to be sent to the first 50 contacts in the address book, meaning that the virus was able to replicate itself astoundingly quickly.
Melissa is now a core part of IT security history due to its wide ranging effects. The vast majority of business enterprise makes extensive use of Microsoft Outlook, Microsoft Word, and Microsoft Excel. Macro viruses can target these applications to cause much damage to businesses and institutions. Melissa had the potential to disable corporate email servers and disrupted companies such as Intel.
A macro virus will usually run automatically when the application is opened. When the virus runs, it can potentially infect the document, other applications, and even other computers. Macro viruses are typically found in phishing links which are clicked on by unsuspecting users. The virus can spread itself automatically by accessing address books and sending itself via email to contacts.
It is important to understand that macro viruses run on software applications and not on operating systems. Macro viruses can be programmed to create new files, edit and move files, format hard drives, insert pictures and more. Like many viruses they can be difficult to detect. Typical signs can include irregularities in documents and a slow computer. Once the virus infects an application, it will typically affect all documents on your computer and can cause irregularities on such documents. You may also be asked to insert a password for certain files and unusual error messages may appear.
There are a number of ways to protect yourself against macro viruses. The most common way to protect against macro viruses (and viruses in general) is by learning some basic habits. Phishing links sent via emails are still the most common way that these viruses spread, so always think twice before clicking on any link sent in an email. The same applies to files that are downloaded. It is never a good idea to run a downloaded file with an .exe extension unless you are absolutely certain that the file has been downloaded from an official source. Be wary of files shared via network or files shared via disk.
Even while taking basic security precautions, it is important to install a high-quality antivirus software. Anti-virus programs are now a necessity and are multi-purpose defense mechanisms against a variety of attack vectors. High-quality antivirus protection programs are available from vendors such as Comodo, Avast, and Total AV. These services will help to detect any kind of macro viruses that are infecting your machine and assist in their removal.
There are free antivirus protection programs available, but generally they will not protect a system effectively as a subscription level service, and at worse they can even install annoying malware on your computer.