Fig.: a type of malware that, hidden in a seemingly useful or harmless computer program,  secretly installs malicious codes or software onto the computer

The "free" game that you downloaded from who-knows-where, turned out to be a Trojan horse: it planted a virus on our computer!

Quel giochino "gratuito" che hai scaricato da chissà dove, conteneva un virus trojan che ha infettato il nostro computer!

In Greek mythology, the Trojan war, as narrated in Homer's Iliad, lasted ten years and was put to an end thanks to the famous stratagem of the Trojan horse devised by Odysseus. The Greeks, pretending to abandon the ten-year siege of Troy, built a huge hollow wooden horse and left it on the beach outside the city as a thank-offering to Athena. The Trojans, thinking that the Greeks were gone, dragged it inside the town walls, unaware that the horse was full of Greek soldiers. At night, the men concealed inside it opened the city gates to the entire Greek army. As a result, Troy was sacked and destroyed