A London-based team of security researchers has exposed a scheme which inserted unauthorised adverts into Google's YouTube.

Spider.io discovered two programmes which placed ads on YouTube's website when viewed by affected PCs. It said the plug-in had been promoted as tools to download videos from the service. It said some directed users to malware.

This was in breach of YouTube's rules.

The firm responsible has been named as California-based Sambreel.

The company did not respond to BBC requests for comment.

However, one of its subsidiaries, Yontoo, told Forbes magazine: "The Best Video Downloader and Easy YouTube Downloader products have been discontinued."

The Financial Times reported that this only happened after Sambreel was alerted to Spider.io's findings.

Injected ads

The security firm - founded by Imperial College London computer scientist PhD graduates - reported that some of the added advert slots had been sold on through exchanges to well-known brands including Amazon, Blackberry, Kellogg's and Toyota. These firms would be highly unlikely to have been aware of this.

However, it added, that others had been bought by "malvertisers" (malicious online advertisers).

BBC News