Suppose you've been accessing American Netflix from outside the UK. In that case, you will most likely have been using a virtual private network (VPN) to make the Netflix servers mistakenly believe you are accessing from inside the country. It's not the biggest crime anyone committed online, but it's technically a bit dodgy. Hola is one such VPN service and is a popular choice for people outside the U.S. who want to watch American content. It also works the other way around with people outside the U.K. who want to access BBC iPlayer content.

How does Hola work?

Hola is a free VPN service that works like most other VPNs, with one crucial difference. To deliver the service for free, Hola uses your computer's idle bandwidth to serve other users instead of paying for and maintaining its own network of servers. It's a P2P VPN effectively. That's how it can offer the service without charging.

So, when accessing Netflix America, you're being routed through a Hola user's computer in America (probably while they're at work or asleep, owing to the time differences). While you're asleep, Hank from Arkansas is catching up on Eastenders. That way, neither you nor Hank has to pay to use Hola, and you can watch the content you want for free.

Hang on, that sounds fair enough. What's the problem?

The problem is that Hola appears to have been flogging surplus bandwidth (yours and Hank's idle computers) to a third party called Luminati. Unlike Hola, Luminati is more than a tiny bit dodgy. Using your computer (and poor old Hank's) as an exit node, they've been carrying out botnet attacks across the Internet.

What's a botnet attack?

It's a means of raising an army of computers to perform a specific, typically malicious, attack, for example, by forwarding massive amounts of spam or executing a distributed denial of service (DDoS) attack by having millions of computers all attempt to access a website simultaneously, bringing it down and preventing the intended users from accessing it.

Oh crap, so now what do I do?

Uninstall Hola. Instructions for this vary according to your browser and operating system, but there's plenty of info online to help you. Google is your friend here.

Even if, as Hola has promised, they never let Luminati access your computer again, your machine remains compromised until you remove Hola. Once used as an exit node, your computer may be hacked or used for spying purposes. Don't take the risk.

I want to carry on watching American Netflix; what are my options?

You can use a server-based VPN network, of which there are many options.

Most providers offer a free tier but do not rely on P2P structures to route traffic. You might be bombarded with adverts, but at least you'll be safe. If you're no longer keen on the free option, you're looking at around £30 a year to use a VPN. If you like sharing your spare bandwidth for good rather than evil, check out BOINIC from Berkley University in America. By signing up for this project, you don't get American Netflix, but you do get to provide spare CPU cycles from your machine to help researchers find cures for diseases, study climate change and generally do good work.