| "M.O.S. (Mystery Operation Squad) is a special operative squad dedicated to investigation on paranormal activity. The nationalities and purpose of the members of the squad are unknown even between mercenaries."|
- in-game description
SIA (Secret Intelligence Agency) is a male character in CrossFire.
SIA features two secret agents, which is the BL and GR side. On the BL side, he has long blonde hair with ponytail and orange sunglasses; his outfit feature long-sleeved white shirt with black tie, light brown vest along with dark green pant. On the GR side, he has gray hair and black sunglasses on his face; his outfit features white shirt with a black tie and dark blue coat, along with lighter blue pant.
- CF China
- CF Vietnam
- CF West
- CF Philippines
- CF Indonesia
- CF Russia
- CF Brazil
- CF Korea
- SIA is the first male character to feature fully finger-covered gloves for both BL and GR model.
- When MOS (Mystery Operation Squad - SIA's name in CF Philippines) was released in the CF Philippines, the character was not fully-detailed. Its long hair and ponytail on the BL side and its spiky hair on the GR side was not present so it only shows the brushed up, flat hair of the character which is being used when the character has a head equipment/gear. The appearance was later changed in a certain update.
- Also in CF Philippines, SIA has an opening price of 150 eCoin. Its price later became 200 eCoin.
- CF Vietnam's description for SIA states that he has "never known defeat, nor anyone survived to tell the tale". Whether this is true or not strictly depends on players using him, although it's mostly impossible to never lose (unless that player only farm Mutation Mode and variants).
- In CF Japan, crates with this character has skin alongside his glasses.
- SIA on the GR side is often portrayed as Global Risk leader in many of CrossFire's CGI movies.