Subdomain

Also known as: sub-domain, host name

A separately named section of your domain (like shop.yourbusiness.com) — handy for organising your presence, but each one is its own door that needs securing.

What it is

A subdomain is a named branch of your main domain. If your domain is yourbusiness.com, then shop.yourbusiness.com, blog.yourbusiness.com and mail.yourbusiness.com are all subdomains — the part before the main name. Businesses use them to separate different parts of their online presence: a shop, a blog, a booking system, a staff login page.

Each subdomain can point to a completely different server or service, run by a different supplier.

Why it matters to your business

Every subdomain is a separate door into your brand, and each one needs its own security. It’s common for the main website to be locked down nicely while a forgotten subdomain — an old marketing page, a trial service that was never removed — sits exposed with an expired certificate or no protection at all. Attackers actively hunt for these.

There’s a particular risk called a subdomain takeover: if a subdomain still points to a service you’ve stopped using, someone else can sometimes claim that service and put their own content on your brand’s address. Customers see your name and trust it. So subdomains are useful, but each is a responsibility, not a freebie.

How to tell / what to do

Check each subdomain you actually use the same way you’d check your main domain — our free checker works on any address you enter, including subdomains. Just as important: keep a list of your subdomains and remove any you no longer use, so there are no forgotten doors left unlocked.