Three times as bad as malware: Google shines light on pay-per-install

The issue of PPI is three times greater than malware: no less than 60 million download attempts every week. That's something that the authors say represents "a major security threat". They estimate as many as five per cent of all browsers have been affected.

Some software builds in a 20-day delay before waking up so users don't immediately associate it with the free download they just installed. Some check in the computer's registry for anti-virus and that they're not already installed.