Abstract: The present invention relates to an anti-theft element in an anti-theft device which is intended to be attached to a theft-attractive article such that said device can only be removed from the article with the aid of a special release device. The anti-theft element includes a fouling-substance ampule which contains a fouling substance and which is disposed in the anti-theft element so as to be broken, crushed or otherwise destroyed or opened so as to release said fouling substance if an attempt is made to release the anti-theft device from the theft-attractive article without the aid of said special release device. The ampule (2) encloses a first fouling substance (B; D; G) having a specific fouling property, and at least one second fouling substance (C; E, F; H) having a fouling property which differs from the fouling property of the first fouling substance (B; D; G).