Admin CP login issues - could it be a hack?

[afullcup]

There are a whole bunch of threads like this on vb.com, but none of the fixes have worked for me (ran tools.php - both domain and resetting admin).

I recently moved servers - once that was complete, I upgraded from 3.6.8 to 3.7 gold. I am still running a test version on my old server.

Settings on OLD server:

path to save cookies: /
cookie domain: blank

I made the new server settings the same, but many members started having login issues where they couldn't stay logged in. It would say "thanks for logging in" and take them back to login. So I changed the cookie domain to ".afullcup.com" which fixed all their issues.

However - now I have this same login issue for the admin CP only. If I get timed out, I am unable to get logged back into the adminCP until I manually edit the database to change the cookie domain back to blank - then login real quick and change it back to .afullcup.com. It's getting a little ridiculous, but I haven't found the culprit.

So, could this be an issue with a hack? I upgraded my old server before the new one - it works fine. No login issues. I don't recall exactly when it started happening in the scheme of all the hack upgrades I've done. There are no hack upgrades on my OLD server, but there are on my NEW server. I am wondering if anyone else had this issue and could possible point me to a hack that could be the offending one. Yes, I've got a lot of them and was just hoping for a shortcut.

Thanks.