This week, the Federal Office for Information Security has again published a warning of the trojan "Emotet"  (only in german)
The trojan accesses old email messages in a victim’s inbox and replies to them, thus jumping into the middle of an existing email conversation. Purporting to be a legitimate correspondent, it sends along a malicious attachment or link. When opening the link or attachment, one receives a message asking to enable the content, which triggers the infection.
If you receive such an email, please delete it. If you are uncertain about the legitimacy of an email, you may call the sender to ask for clarification.
Please feel free to contact us by firstname.lastname@example.org, if you have any questions.