Q:

Were any of Weasley twins' products used by Voldemort partisans or generally for evil purpose?

Were any of Weasley Wizadring Wheezes' (Fred and George Weasleys') products used by Voldemort partisans or generally for evil purpose? It seems like some of their stuff could be used for less than "good" purposes, e.g. extendable ears.

A:

There was at least one case of this happening.
Peruvian Instant Darkness Powder was used by Death Eaters at the end of HBP to help get into Hogwarts,

 where they were meant to kill Dumbledore

The scene is where Ginny/Hermione/Ron are telling Harry how Death Eaters led by Malfoy were able to get into the castle despite them patrolling:

From "The Half-Blood Prince", Chapter 29 - "The Phoenix Lament"
'He came out of the Room about an hour after we started keeping watch,' said Ginny. 'He was on his own, clutching that awful shrivelled arm –'
'His Hand of Glory,' said Ron. 'Gives light only to the holder, remember?'
Anyway,' Ginny went on, 'he must have been checking whether the coast was clear to let the Death Eaters out, because the moment he saw us he threw something into the air and it all went pitch-black –'
'– Peruvian Instant Darkness Powder,' said Ron bitterly. 'Fred and George's. I'm going to be having a word with them about who they let buy their products'
'We tried everything, Lumos, Incendio,' said Ginny. 'Nothing would penetrate the darkness...'

