In these days of working from home it's become increasingly common to share Internet connections with other people. But how can you be sure it's safe to do so?

"If you want to share your Internet connection, you should keep the router up to date and install regular security updates to ward off hacker attacks," says router specialist Keywan Tonekaboni.

The easiest way to share WiFi is by using guest access, a function available on most devices. All users need to do is call up the relevant network.

"The owner then confirms that the guest is legitimate, and that's about it," says Rainer Schuldt from Computer Bild magazine. Fiddly password entries are generally not required.

Most routers now offer the option of activating such a guest network, which works separately from the main network.

"The guest WiFi can also be secured so that, for example, you can only check emails," Tonekaboni says.

"Attacks from outside should always be blocked by a firewall," Schuldt says.

Most common router models have an integrated firewall to prevent unauthorised persons from accessing the home network and its computer from outside.

It can be set up so that certain ports are opened up for external traffic, for example for playing online games.

Then there are the so-called free or DIY networks in which people come together to share their Internet access.

Each user in the network provides their wireless LAN router for data transfer to other participants and in return, the user can transmit data through this free network.

But what if a guest uses your WiFi to do something illegal such as downloading pirated movies? The legal consequences depend on the laws in your country, but there are some steps you can take to protect yourself.

If you do allow guests to use your network, you should take some precautions such as assigning secure passwords or blocking certain websites, according to Oliver Buttler, a consumer rights advocate in Germany.

"From a legal point of view it makes sense, for example, to record everything in the case of changing flat-sharing residents and, if possible, assigning different passwords," he says.

 - dpa