I think you'll find - and Mixture can shoot me down if I'm wrong, cos he knows a lot more about this than me - that Avast! is flagging up long-term security and vulnerability issues with Adobe and Java. I know that Apple won't allow the use of some versions of Java, and I recall that I had the same issue as Gemma when working on my friend's pc. This was posted on the web in December 2012.:
According to the recently published Kaspersky Security Bulletin 2012, Oracle Java was the most frequently exploited software by cybercriminals during the year, with Adobe Reader and Adobe Flash Player ranking in the second and third places, respectively.
Exploiting vulnerabilities is one of the primary methods used by cybercriminals to install malware on victims’ computers. Cybercriminals exploit applications or software that have un-patched security vulnerabilities, which exist because either the individual or business have failed to patch their vulnerable applications with the latest security updates from vendors.
Exploit packs – or malicious programs that try to infect a computer utilizing various vulnerabilities in popular software – are the main tool behind web-based attacks.