Eavesdropping is the act of intercepting communications between two points.

In the digital world, eavesdropping takes the form of sniffing for data in what is called network eavesdropping. A specialized program is used to sniff and record packets of data communications from a network and then subsequently listened to or read using cryptographic tools for analysis and decryption.

For example, Voice over IP (VoIP) calls made using IP-based communication can be picked up and recorded using protocol analyzers and then converted to audio files using other specialized software.

Data sniffing is easily done on a local network that uses a HUB since all communications are sent to all the ports (non-recipients just drop the data) and a sniffer will simply accept all of the incoming data.

This goes the same for wireless networking where data is broadcast so even non-recipients can receive the data if they have the proper tools.

Actual eavesdropping, that is the simple act of listening to other people talk without them knowing it, can be done using current technology such as hidden microphones and recorders.

Hacking into devices such as IP phones is also done in order to eavesdrop on the owner of the phone by remotely activating the speaker phone function.

Devices with microphones including laptops and cellphones also can be hacked to remotely activate their microphones and discretely senddata to the attacker.