Botnets are groups of hijacked private and corporate computers controlled remotely and which are used, among other things, to send spam, usually without the user’s knowledge. Undetected, the installed malware often only runs in the background, making it more difficult for users to identify the risk and react accordingly. It is currently estimated that over 90% of all spam e-mails are distributed via botnets.
E-mail with malware as an attachment
The infection takes place through malware known as Trojans created specifically for the purpose of infection. The “classic” infection pathway is through e-mail attachments. The user is led to believe that the attachment contains essential information or an important document, such as an invoice, a tax form, or a package delivery notification. Instead, it contains malware that is activated as soon as the user attempts to open the attachment.
Unknown file attachments should therefore never be opened. The option “Hide extensions for known file types” should also be deselected in the system settings; doing so ensures the detection of a fake PDF file with the file extension pdf.exe.
A further infection pathway that has recently become more popular is drive-by malware. The malware is located on a manipulated website. When the site is opened in a web browser, the Trojan is installed on the user’s computer (drive-by). The malware is commonly disseminated via spam e-mails that contain links to the infected websites. If the user clicks on the link, the malware is installed in the background. Particularly popular lures include sites like Facebook, Twitter, or YouTube.
A message that feigns an important message, messages from friends, or a newly uploaded video is sent to the user in the hope that he will click the enclosed link. Users should never click on links in e-mails unless they can be one hundred percent sure that the message is real.
Plug-in and application risks
Hazard: data storage devices
A further risk that can lead to botnet infection is the use of external data storage devices like USB sticks or SD cards. Because most people aren’t able to recognize what is happening in the background during opening, the rule is: unknown data storage devices should always be checked by an up-to-date virus scanner before use.
Users should also avoid using data storage devices that are not their own whenever possible. In addition, the Windowes option to automatically always treat a certain type of device, such as a USB stick, the same way when inserted, should be deactivated.
Spam and virus protection
Despite all precautionary measures, when it comes to avoiding botnet infections, the most important element is reliable spam and virus protection. Users should check which spam and virus protection options are offered by their e-mail provider, e.g. their Internet provider or webmail service. A virus scanner should also be installed. Important: always keep the virus scanner up to date!