Nod32 has been on a false detection rampage this week. It thinks that Cityofheroes.exe has a virus within it. This is very rare, but inevitable for any heuristic antivirus. Avast! insisted that Quake 3 was a deadly trojan last year. I've had Nod32 for going on 6 months now, and this is the first time it's bitten me.
You need to enable advanced settings, get into the setup tree, find the exceptions list, and add your City of Heroes directory to it. That will ensure that Nod32 doesn't interfere with CoH.
It's well worth sticking with Nod32, because it's still the best AV out there in my opinion.
Necrobond - 50 BS/Inv Scrapper made in I1
Rickar - 50 Bots/FF Mastermind
Anti-Muon - 42 Warshade
Ivory Sicarius - 45 Crab Spider
Aber ja, nat�rlich Hans nass ist, er steht unter einem Wasserfall.
I have Nod32 aswell and i had the same problem.
So to be able to log in i turned off the virus protection while i loaded up COH then turned it back on. . . . . this seems to have corrected the issue. 
Well untill it all goes bog-eyed again 
Aptum KM/SD scrapper (Defiant) Aptum brute (freedom) Aptum MA/SR scrapper (union)
Aptum. DB/Regen scrapper (union) Frank Murphy MA/SD scrapper (defiant)
Dirk Dark Thug/FF MM (defiant) Grunt-503 AR/Dev blaster (defiant)
Hot-HunterZ Kin/Fire controller (defiant) HunterZ Claw/Inv scrapper (defiant)
Kniteborne Stone/Mace tank (defiant) Knitemare PB (defiant) Seer Martinez Widow (defiant)
So i've been unable to login since the patch. I get the ole' checksum error which seems to have started because of my AV - Nod32.
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Anyway, I added CoH to the exclusions list. Reran the patch. Checksum error
I deleted the checksum and lock files. Reran the updater, CHecksum error
I deleted the updater, downloaded the last EU updater I could find. CHecksum error
I raised a ticket. Renamed the piggs and data files. Reran the EU updater. Checksum error
I deleted the install, installed from DVD, EU Updater, Checksum error
I searched the HDD and registry for all COx and CityO files. Removed them. Deleted the install. Reinstalled from DVD. Ran the EU updater per the excellent post I found somewhere else here. Checksum error.[/list]
I've now just downloaded a clean EU Updater and run that. 2.5g patch now being applied...
Any thoughts, hints or ideas at this point greatly appreciated. I'm just shy of 35 on my Ill/Storm Trolly and wants me Tornado!