The questions (below) I suspect to be relatively easy to answer - and they will improve my knowledge substantially...
Background: My Windows 7 machine started freezing. Following several forced power off situations other problems arose (with booting - now resolved). The last time it froze was while in BIOS settings so I'm working on an assumption that these issues are hardware related (it's a cobbled together machine not one off the shelf. During troubleshooting I ran MalwareBytes for the first time, which seems to have prompted AVG into noticing two problematic files (AVG calls these 'Exploit_c.VRA' and 'Script/Exploit.Kit.AF') AVG was happy to remove these. Further scans (MalwareBytes/AVG) find nothing.
- The problem files were in Firefox's cache (Mozilla/Firefox/Profiles/...../Cache) - does that tell me anything about whether they were executed/used?
- These are in my wife's account - which does not have admin status - does this mean things are relatively safe?
- Is the 'last modified' date on these files likely to be the date they were downloaded (my guess is that it is)?
- The 'last modified' date for these files corresponds to an evening of web browsing by my wife. Is there any way to work back to find out what these files were - to confirm they were downloaded then (no downloads are listed, if it was a pdf file it would have appeared in a browser plugin not as a downloaded file)?
- My wife has not done anything online of consequence (e.g. shopping/banking) since the last modified date, so is it likely that no sensitive data is compromised? (I did some shopping in a separate non-admin account).
- If trojans (etc) allow people to execute their choice of code on a computer does this mean that they could (are likely to) find ways to install stuff or access stuff which isn't listed in antivirus databases? Or does it make it possible to open up the computer for remote access or something? Or does a clean antivirus/malware scan tell me that it's likely that things are now safe?
- Scans on a separate Windows XP computer (physically networked to the problem machine, but without intentionally opening up any communication) show nothing. Can I relax about this one?
- An old (well out of date) imac on the same physical network (but not opened up for communication) has no AV scanners on it. Do I need to be doing something proactive to check that this is safe?
I'd really appreciate advice and comment on these issues. Fundamentally the answers will give clues on a way forward for me. I'm thinking that the answers themselves are probably relatively simple for someone who knows their stuff - but I realise that reading this will have taken time so thank you again.