By the following measures you will substantially increase your device's protection against external threats.
You may already be using anti-virus software but to be effective the software should be updated on a regular basis with the latest virus definition files.
From time to time developer of operating systems release 'patches' to correct vulnerabilities in their programs. These weaknesses are regularly exploited by virus writers and hackers to gain unauthorized access to those devices that have not been patched. To check for patches and updates you should visit the developer's website, typically in their Download section.
A 'firewall' is another small program that helps protect your device and its contents from outsiders on the internet. When installed it stops unauthorized traffic to and from your device. Appropriate Software is offered in stores or on the internet.
Geeignete Programme für Ihr Gerät erhalten Sie im Fachhandel oder über das Internet.