This question is not an easy one to answer. Generally, bots are designed to be as inconspicuous as possible and to not hinder the normal use of an infected device in any way. High-performance end devices and fast Internet connections largely compensate for the additional system resources that the bot uses. However, some bots come coupled with other malware infections, and these infections may make their presence known with unusual occurrences such as unwanted pop-up advertisements or system messages that you haven't seen before. Sometimes, an active bot that is executing its remotely issued commands may noticeably impair the performance of the system.

Possible symptoms of an infection

So, what else might indicate that your device has been infected with malware? If you fall victim to an attempt at extortion viaransomware, then there is no room for doubt: The locked screen and demand for payment is a clear enough indicator. But if your computer suddenly starts running extremely slowly with no clear reason, your fast Internet connection grinds to a halt or the battery on your smartphone reaches empty much quicker than it used to, this could all point to malware activity taking place in the background.

You should also be suspicious if your network traffic is suddenly unusually high, or if you start to notice an increase in advertising pop-ups on websites that used to be free of ads. The same applies to any changes in browser settings that you didn't make yourself - such as new bookmarks or a different home page.

Just like any other piece of software, your browser needs to be kept up to date to eliminate security vulnerabilities. The BSI recommends installing any updates from the manufacturer as soon as possible after release. It is also a good idea to regularly remove out-of-date, unknown and unused apps from your system on a regular basis as a preventive measure. Advanced Windows users can also use a Linux live CD regularly to scan for potential attacks.

Do not ignore messages and warnings!

Malware can go unnoticed for a long time if the signs of infection aren't as obvious as a ransomware-locked screen or a warning from your anti-virus software. The infiltrator can continue to cause damage all this time - perhaps by integrating a PC or smart TV into a botnet so that it can be exploited remotely in a denial-of-service attack, or used to send spam e-mails. Keep an eye out for reports in the media and take note of any official warnings issued by the authorities.

Many people still ignore information about specific cyber threats. The Avalanche botnet, for example, was widely reported in the press. Once the botnet had been successfully taken down at the end of 2016, Internet providers and the BSI joined forces and used data from a sinkhole server to warn potential victims and advise them to scan their systems. Those affected even received personal letters from their providers - and yet the infection rate had still stalled at 39 percent of the original value one year later.