Posts on HeidelSec

What does a security audit cost? How the price is formed – and what a good offer looks like

Tue, 15 Sep 2026 10:00:00 +0200

What drives the effort of a security audit, why a serious fixed price does not exist, and how to recognise a good offer.

Security Audit vs. Penetration Test: The Difference – and Which One Is the Right First Step

Mon, 14 Sep 2026 10:00:00 +0200

Security audit or penetration test – what is the difference, when does each make sense, and where should you start? An honest assessment.

What Does a Pentest Cost? How the Price Is Built Up – and What to Look for in a Proposal

Mon, 14 Sep 2026 10:00:00 +0200

Why there is no fixed price for pentests and security audits, which factors drive the cost, and how to recognise a serious proposal.

Ransomware: Will your backups hold up when it hits?

Sun, 13 Sep 2026 09:00:00 +0200

Ransomware targets your backups first. The 3-2-1 rule, the mistakes that happen most often – and a 5-minute check of your own defences.

Does NIS2 apply to you? The 5-minute check for your company

Sat, 12 Sep 2026 10:00:00 +0200

NIS2 affects far more companies than many expect. How to assess within five minutes whether your company falls in scope – and what to do next.

Excel Analysis with Pandas – Quick Statistics Without Formulas

Sat, 21 Feb 2026 09:00:00 +0100

Why Pandas Instead of Excel Formulas?

Excel is ideal for simple tables, but with larger datasets it quickly becomes unwieldy. With Pandas, you can read, analyze, and statistically evaluate Excel files – reproducibly and automatically.

Installation

pip install pandas openpyxl

openpyxl is required for Excel files (.xlsx).

Reading Excel Files

import pandas as pd

# Read Excel file
df = pd.read_excel('sales_data.xlsx', sheet_name='Revenue')

# First look at the data
print(df.head())
print(df.info())

Important parameters:

sheet_name='Name' – Select specific worksheet
usecols='A:E' – Read only specific columns
skiprows=2 – Skip first rows

Basic Statistics

# Quick overview
print(df.describe())

# Individual statistics
print(f"Average: ${df['Revenue'].mean():.2f}")
print(f"Median: ${df['Revenue'].median():.2f}")
print(f"Minimum: ${df['Revenue'].min():.2f}")
print(f"Maximum: ${df['Revenue'].max():.2f}")
print(f"Total: ${df['Revenue'].sum():.2f}")

Output:

Understanding and Implementing DNSSEC Correctly

Fri, 20 Feb 2026 10:00:00 +0100

DNSSEC protects against DNS spoofing and cache poisoning. Learn how DNSSEC works, common mistakes, and how to implement it correctly.

Download a Complete Website with wget

Fri, 08 Nov 2024 15:30:00 +0100

Saving a Website for Offline Use

Using wget, you can download an entire website for offline access with this command:

wget -rkpNc -e robots=off http://www.example.com/

Parameters Explained

-r: Download pages recursively.
-k: Adjust links for local viewing.
-p: Fetch all resources (images, scripts).
-N: Only download new or modified files.
-e robots=off: Ignore robots.txt restrictions.
-c: Continue the download if interrupted.

With this command, wget reliably saves the entire site for offline use.

cAdvisor on Synology

Thu, 07 Nov 2024 10:30:00 +0100

cAdvisor on Synology

Running cAdvisor in Docker on Synology was a challenge, as it often wouldn’t start despite no changes to the launch options. The issue turned out to be related to the inotify settings.

The Problem

When running the following command to start cAdvisor:

docker run --name=cadvisor \
 --volume="/:/rootfs:ro" \
 --volume="/var/run:/var/run:ro" \
 --volume="/sys:/sys:ro" \
 --volume="/var/packages/ContainerManager/var/docker/:/var/lib/docker:ro" \
 --security-opt no-new-privileges=true \
 --restart=on-failure:5 \
 google/cadvisor:latest --docker_only=true

cadvisor:
 image: gcr.io/cadvisor/cadvisor:latest
 container_name: cadvisor
 read_only: true
 security_opt:
 - no-new-privileges=true
 command:
 - "--docker_only=true"
 volumes:
 - /:/rootfs:ro
 - /var/run:/var/run:ro
 - /sys:/sys:ro
 - /var/packages/ContainerManager/var/docker/:/var/lib/docker:ro
 restart: on-failure:5

I encountered the error:

My first blog post

Sat, 25 Mar 2023 10:30:00 +0100

This is the first blog post on my new website. I am very excited to share my thoughts and ideas with the world!

What I will cover in this blog

I plan to write about several topics in this blog, including:

Automation
Data Science
IT Security

I hope you are interested in some of these topics and that you will enjoy my future posts.

Until next time!