Whilst most virus killers and popup-blockers behave sensibly with Quoox out-of-the-box, some can be a bit “over zealous” and can interrupt critical Quoox processes.
You should ideally whitelist “my.quoox.com” in your virus killer/popup-blocker so that the operation of Quoox is not interrupted.
This is particularly important for Norton Anti-Virus, where we have become aware that Norton can intercept the payment process – which might result in a payment being charged, but the outcome failing to be received by Quoox. The Norton process returns the user to the charging process, but this can result in the member being charged twice – as Quoox is only being “aware” of the second payment (due to the first being intercepted).