Is my Mac compromised?

Sometimes a window pops up on my Mac mini and disappears before I can see what it is about. I am not even sure it is browser related. Is my Mac compromised? Is it a virus? How can I find out which program is responsible for the popup? How can I check if my Mac doesn't have a virus, worm, trojan, ...? I usually check downloaded files with ClamAV, but nothing was ever found.

thanx

No Mac OS viruses exist in the wild - so not your issue. But when does this 'popup' occur, i.e. are you in a browser (if so, a specific website or multiple ones) and/or does it appear while doing some other activity on the computer?

Not sure if checking the 'Logs' would help (see attachment for my MBPro; About this Mac -> More Info ->System Report) - I'm still finding them rather confusing (just 6 months on Mac OS), but hopefully our more experienced members & mods will 'chime in' w/ advice! Good luck - Dave

Does this popup occur at any particular time or with any particular service or application(s)? It could very well be an application that is opening and closing windows to accomplish things. For example, the Mendeley referencing application requires that it be open when you use their Word plugin so it will quickly flash open if it isn't already. A similar thing happens with Tracks (an application that lets you quickly play tracks from iTunes with a Spotlight-esque interface) - it has to open iTunes if it isn't already open and this causes iTunes to flash on screen briefly.

Also Dropbox flashes a window briefly on startup/login. Could be anything.

I have a VPN(Private Internet Access) which does the same thing when shutting down my laptop. A real brief flash before it shuts down. Nothing to worry about.

In any event, member RadDave's suggestion is a good one, and that is to scan through your logs to see if anything shows up. Otherwise, don't worry about it.

Thanx for the advice. Feel less worried. I have Dropbox, so that might be 1 answer. It doesn't always happen when I am using a browser, but this morning it did. I had opened a couple of sites when a popup screen appeared and immediately disappeared. I tried opening the sites one by one but nothing happened.
I scanned my entire homedir and ClamAV did find some (forgot the complete name) phishing emails which were in spam folders and a pdf, which I hadn't opened yet with a metasploit.
Going to keep an eye on those log files when it happens again.