IT & Security Professional · Nurmijärvi, Finland
KAJ
KUOSMANEN
Network Infrastructure · Linux · Cybersecurity

Experienced IT and information security professional with over 20 years of hands-on experience across network infrastructure, systems administration, and cybersecurity. Background includes 12 years in the Finnish Navy as an IT specialist, with operational-level responsibility for network design, firewall management, and server infrastructure. Methodical, reliable, and comfortable in both technical and client-facing environments.

Linux / Ubuntu Docker Firewalls WAN/LAN Cisco · Juniper Finnish Navy, Ret.
Get in touch
Kaj Kuosmanen HackTheBox Badge

// Skills

◈
Linux & Systems
Ubuntu Server · Debian
SSH hardening · UFW · fail2ban
Nginx · Docker · Docker Compose
Bash scripting · Cron automation
VMware virtualisation
◎
Security
Server hardening · Log analysis
Intrusion detection · Honeypots
OSINT · Shodan
HackTheBox — Hacker Rank
StoneGate / Stonesoft firewall
⬡
Networking
WAN/LAN design & administration
TCP/IP · Ethernet troubleshooting
Cisco IOS · Juniper JunOS
BGP · OSPF · IS-IS · MPLS
HP enterprise switching
▦
Infrastructure
Reverse proxy · SSL/TLS
DNS management · DDNS
Uptime monitoring
Portainer · Container orchestration
Linux & Windows servers
◷
Tools
nmap · Wireshark
Git · GitHub
Let's Encrypt · Certbot
Shodan API
OpenVAS · Burp Suite
◐
Languages
Finnish — Native
English — Professional
Swedish — Basic

Bash · Python (learning)

// Experience

2025 — Present
Security Guard
X-Sec Oy · Citymarket Tammisto
Continued at the same site after employer transition — store manager and department head personally requested to remain. Customer service, access control and incident prevention in a large retail environment.
2021 — 2025
Security Guard
Securitas Oy · Citymarket Tammisto
Started on a flexible contract, moved to full-time employment in November 2022. Customer interaction, loss prevention, and emergency response coordination.
2013 — 2021
Bookkeeper / Accountant
Tilikirjurit Oy
Minority shareholder and full-time bookkeeper in a family-owned practice. Full-cycle accounting, payroll processing, VAT and tax filings for SME clients.
2010 — 2013
IT Support Specialist
École franco-finlandaise d'Helsinki
End-user support for teaching and administrative staff. Network and server infrastructure maintenance.
2002 — 2010
IT Designer / Network Specialist
Finnish Navy — Operational Department
Designed and maintained enterprise network, firewall, and server environments at operational level. Developed and documented IT security architecture and policies. Led and contributed to defence-sector IT procurement and integration projects. Expert-level consultation across Finnish Defence Forces IT initiatives.
1998 — 2002
IT Officer / Signals Officer
Finnish Navy
Operational responsibility for IT systems at unit level. Management of communications networks and data links. Reserve officer rank: Senior Lieutenant (Yliluutnantti).
2017 — Present
Volunteer — Security & Infrastructure
Disobey — Finland's Premier Hacker Conference
Annual volunteer at Finland's largest hacker and security conference. Supporting event infrastructure, technical operations, and community engagement in the Finnish security ecosystem.
2019 — Present
Member since founding
HelSec ry — Helsinki Cybersecurity Community
Member of HelSec since its founding in 2019 — Helsinki's cybersecurity community organisation running regular meetups, workshops, and talks. Active participant in the Finnish information security scene.

// Education & Certifications

Formal Education
  • Security Guard Certificate · Hyria2021
  • Bookkeeping & Accounting · Markkinointi-instituutti2013–2014
  • IT Technician (Datanomi) · AmiEdu2003–2005
  • NCO · National Defence Institute1992–1994
  • Finnish Matriculation · Laanilan lukio1990
Cisco & Juniper
  • Configuring Juniper Networks Routers M/T-series2006
  • Building Scalable Cisco Internetworks (BSCI)2003
  • Interconnecting Cisco Network Devices (ICND)2002
Cygate Academy
  • BGP Fundamentals2005
  • MPLS Fundamentals & VPN2005
  • IS-IS Routing2005
  • OSPF2003
  • Router Fundamentals2002
Security
  • Certified StoneGate Engineer (CSGE)2006
  • StoneGate Fundamentals & Implementation2006
  • StoneGate Advanced Implementation2006
  • Cyber Security Base MOOC · U. Helsinki × F-Secure2017–2018
  • HackTheBox — Hacker RankActive

// Projects

Live Infrastructure
Bluestorm Lab Server
Publicly accessible Ubuntu Server 24.04 running a hardened stack: SSH key auth, UFW firewall with subnet-level blocking, fail2ban, Nginx reverse proxy, Let's Encrypt SSL, Docker, and real-time uptime monitoring. Endlessh SSH tarpit on common attack ports.
Visit lab.blackrose.fi →
Web Application
QSO Map
Full-stack PHP/MySQL/Leaflet.js application for amateur radio contact logging and visualisation. Band-coloured contact dots, live PSKreporter propagation, statistics panel, CSV/PDF export, country counter with flags. Self-hosted on personal infrastructure.
Visit QSOmap →
Security Community
Disobey Volunteer
Volunteering since 2017 at Disobey — Finland's largest hacker and security conference held annually in Helsinki. Contributing to the Finnish information security community through technical event support.
Security Community
HelSec ry — Member since founding
Member of HelSec since its founding in 2019 — Helsinki's cybersecurity community organisation running regular meetups, workshops, and talks. Active participant in the Finnish information security scene.
Continuous Learning
HackTheBox — Hacker Rank
Active participant on HackTheBox achieving Hacker rank through completed machine challenges. Practical offensive and defensive security skills through real-world simulated environments covering penetration testing, privilege escalation, and CTF challenges.
View HTB profile →

// Contact

Let's work
together.

Available for sysadmin, network engineering, and security-focused infrastructure roles. Based in Helsinki, Finland. Open to both Finnish and international opportunities.

Location Nurmijärvi, Finland
Amateur Radio OG2KAJ
Lab lab.blackrose.fi
HackTheBox RoseBlack