Artist Ai Weiwei, feminist punk rock protest group Pussy Riot, and NSA whistleblower Edward Snowden have joined forces with Amnesty International and AdBlock to appear in online ads protesting against censorship.

The ads are available to AdBlock's 40 million users today (March 11), who will be asked if they want to see messages from Amnesty International where ads they block would usually appear. Users can then click through to content from 'people who governments have tried to silence'. Weiwei's message reads 'Without freedom of speech there is no modern world, just a barbaric one', while Snowden says 'Even if you're not doing anything wrong, you're being watched and recorded'.