Spam filters registering clicks?

There are several posts here on Marketo about this issue, and my firm has been digging into it a lot over the last few days. The short answer is that yes, this does indeed happen - spam filters (like Barracuda) / bots / junk mail algorithms do indeed click on links in emails (see this interesting blog post from 2013 regarding the issue - Barracuda calls this "multilevel intent analysis"). The spam filter is looking for redirection or malware or something like that. There isn't a whole ton that we marketers can do about it, though. Here is what we've done and found:

• First thing we did was download the entire Marketo activity log using the API, put it in a database, and started dissecting the "Click Email" event types. We also sat down with the system administrator here to review some of this data. In short: there is nothing in the User Agent, Platform, Device, etc. that will help spot these.
• Then we started looking at the timing: what about people who click before they open? What about people who click really quickly after the "Send Email" activity is logged? Well...the "Send Email" event isn't indicative of when, exactly, the email leaves Marketo's servers, so that's not really accurate - you can't spot bots based on that.
• The best way we've found right now is to include a one-pixel picture / link on the email - invisible to just about everyone (as suggested here). Anything that clicks on such a tiny little pixel you can consider a bot. True; someone might not load images and see a box, but most people won't see it at all.
• Another possibility: see if you have a bunch of clicks that all happen at the same time (or people clicking every link in an email, every week - would a real person really need to read your Privacy Policy week-in and week-out?). Those are probably bots...but I personally would want to download the data into a real database before attempting this kind of query.
• One more (really complex) possibility: when we went to our sysadmin (the guy who runs our own company's Barracuda machine) about a lot of these issues, he started to "ping" some of the IP addresses included in the suspicious "Click Link In Email" activities. One or more of them shot back a response indicating that it was a Barracuda box. If you are really, super-duper concerned with this problem, it should be possible to download all Marketo activities via the API and write some custom script / code to extract the IP addresses from the Marketo "Click Email" events and then to periodically ping all these servers to see if you can get them to self-identify as a spam filter (parse the text-strings of the responses for incriminating evidence).

We have not done this last thing, as our "one-pixel" solution has indicated (at least over the last two weeks) that it's likely not a major issue. Perhaps some day, when our organization has unlimited resources (heh), we will pursue this last option, but the reality is that we have a lot going on and better things to do to add more value to our marketing efforts.

I would also like the data to exist in a perfect world - one where our Users validate our TRON Data Discs and we can take down the evil Master Control Programs while we're on our light-cycles on the grid - but that gleaming world of perfect, neon data does not exist. For most of us, I would guess this statistical aberration will not significantly affect our analysis of content effectiveness.

Hope this helps.