 In the last decade, a practice called knitting graffiti, guerilla knitting, or yarn bombing— the use of knitted or crocheted cloth to modify and beautify one's (usually outdoor) surroundings—emerged in the U.S. and spread worldwide.Magda Sayeg is credited with starting the movement in the US and Knit the City are a prominent group of graffiti knitters in the United Kingdom.Yarn bombers sometimes target existing pieces of graffiti for beautification.