Yes! This is a weed.

Oxalis pes-caprae (Soursob, Oxalis) is a very invasive plant that produces a main tuber-like root, plus several small bulbs. It has trifoliate heart-shaped leaves with brown or purple spots on top. The flowers area vivid lemon yellow in colour. It occurs widely throughout the cooler regions of Australia and is mainly a problem in gardens.

Control is by removing the entire plant including bulbs. Due to the numerous small bulbs, this can be a very tedious task. Glyphosate can be applied in spring, summer and autumn. Heavy mulching can be effective.