what happened to my security?

libre office crashed last night, then I had some java problems on firefox. there were many dodgy looking enties in java cache. so i emptied it. System was slow, been fine until last night.
updated and ran a full scan with avast (pup on)it found nothing (nor did hitman pro)
Removed avast installed my previous av which I have a few months left on it found 16 trojans, created on 6 different days over the last few months, they were duplicated on my external hdd which I use for back ups.
I would usually expect these to be left over bits, but avast has never detected anything!
I now have the following in quantine (all missed by avast.
trojan maljava
trojan bredolab
virus infostealer
info stealer bancos
w32 koobface
5x trojan.gen
2 x trojan gen.2
trojan gen downloader

what gives? I guess these are probably all related, but creation dates are 3 months apart?

No way to tell on the limited information you have given.

What was the other AV and what type of scan ?

What were the infected file names, where were they found e.g. (C:\windows\system32\infected-file-name.xxx) ?

its nis 2011 deep scan, C:users\me\appdata\locallow\sun\java\deployment\6.0\45\ that’s where trojan maljava was. All the others, strangely (18) are in F:me\backupset\back up files ‘date’ zip it’s these that have the three different dates.
windows 7 64 clean install 3 months ago, only had avast pro them avast is. and hitman pro

Well unless you specifically have avast scan archives they aren’t scanned.
Archive (zip, rar, etc.) files are by their nature are inert, you need to extract the files and then you have to run them to be a threat. Long before that happens avast’s Standard Shield should have scanned them and before an executable is run that is scanned.

If your JAVA version is up to date then there is less of a likelihood of exploits in the JAVA cache ?

I rarely take anything on face value and I would always check detections at somewhere like virustotal.com.

Yes, I will do that I think. Thanks for the help.

You’re welcome.