Alleged Flash Player zero-day used in Angler exploit kit
Adobe 'investigating reports'.
Vulnerable browser plug-ins are one of the most important infection vectors, which is why it is so important to keep them up to date. If you don't, visiting a website infected with an exploit kit (a toolkit that attempts to exploit a number of vulnerabilities at once) could result in malware being dropped on the computer through a drive-by download.
The good news, however, is that keeping plug-ins fully patched usually suffices for the average Internet user: developers of exploit kits rarely 'burn' zero-days when targeting the general public.