I tried to measure a donation goal on a PayPal form, and after a few days, Piwik says "$ 3.40282E+38 overall revenue" and breaks when requesting any details (the breakage is due to bug #1847). After deleting the goal and replacing with a new one, it works normally for a short while, then shows 3.40282E+38 revenue again. The donation numbers seem correct, only the revenues are affected.
3.40282E+38 is the maximum value a float can hold, so maybe this is some sort of conversion error? The revenue is logged manually via @piwikTracker.trackGoal@, and the second parameter looks like this: @10000.00@
Can you query your log_conversion table, and see what's being recorded in the revenue column?
There are a lot of numbers that correspond to real donations, and a few obviously wrong ones. Currently, two days after the last time of deleting old results and starting anew, there are two such records, along with ~100 real ones: 1.5e+07 and 9.99e+11. (It is possible these are pranks, or attacks of some sort; some could just type in some very high number, click Donate and close the Paypal window which comes up next without donating. I cannot imagine who would bother with that, though.)
Why not append the revenue to the return url, and trackGoal on the confirmation?
I would advise, like vipsoft, to check for the amount on the client side. This wouldn't prevent users faking the request to piwik.php directly, but I'm not sure how we could avoid these (arbitrary revenue threshold below/above which we ignore the conversions? User defined range of valid revenues?)
wontfix for now, can reopen if problem occurs again