tamper

Concise Oxford English Dictionary © 2008 Oxford University Press:
tamper/ˈtampə(r)/

▶verb (tamper with) interfere with (something) without authority or so as to cause damage. ▶noun a machine or tool for tamping down earth or ballast.

– derivatives
tamperer noun.

– origin C16 (in the sense ‘busy oneself to a particular end, machinate’): alt. of the verb temper.