It was an early form of consumerization with people bringing the applications they used in their personal lives into the workplace. Call it a “BYOA” approach: Bring Your Own Application. Always being ready to adapt to emerging trends, attackers started crafting malware that would exploit the weaknesses these new applications introduced into the workplace. Attackers adapted methods that worked so well with email worms like the ILOVEYOU worm of 2000 to create a new kind of worm that could spread even faster over IM networks.
Read more, a MUST:
Via Gust MEES