I don't think I have had this problem or am I a security expert.
If it was me I would get in contact with the administrators of the Forum in question. Give them what information you have about this hack attempt.
If anybody else has use of your computer I would be asking some questions.
I would also change my password on the Forum in question.
My Computer
At a glance
Windows 10 Pro. 64/ version 1709 Windows 7 Pr...Intel i7-6800K @ 4.3Corsair Platinum 16 gig @2400EVGA GTX 1070 OC
Computer type
PC/Desktop
Computer Manufacturer/Model Number
Home made Desktop
OS
Windows 10 Pro. 64/ version 1709 Windows 7 Pro/64
CPU
Intel i7-6800K @ 4.3
Motherboard
ASUS X-99 Deluxe II
Memory
Corsair Platinum 16 gig @2400
Graphics Card(s)
EVGA GTX 1070 OC
Monitor(s) Displays
Asus 27" LED LCD/VE278Q
Screen Resolution
1920-1080 or 1280-720 HDMI
Hard Drives
INTEL SSD 730-240 Gb Sata 3.0/
PSU
EVGA Platium 1200W
Case
Phanteks Luxe Tempered Glass 8 fans/ one radiator
Cooling
XSPC/ Water Cooled CPU
Keyboard
Das 4 Professional
Mouse
Logitech M705/MX Anywhere 2-S
Internet Speed
100 mbits
Antivirus
Microsoft Security Essentials/ Malwarebytes Premium 3.0/ SAS
Browser
I.E. 11 default/Firefox/ ISP Time Warner Cable/Spectrum
Other Info
LG BluRay Burner/
Sound system-KLipsch-THX/
Icy Dock ssd Hot Swap bays.
I think that everything worked the way it was supposed to, and I agree that you should change your password on a regular basis. Change it now, just to be sure that they weren't successful on that sixth attempt, but otherwise, I think the forum did what was supposed to happen when an errant login attempt was made.
My Computer
At a glance
Microsoft Windows 10 Home Build 15036Intel(R) Core(TM) i7-860 @ 2.80GHz4.00 GBNVIDIA GeForce GTX 750
Computer type
PC/Desktop
Computer Manufacturer/Model Number
iBuyPower NZXT
OS
Microsoft Windows 10 Home Build 15036
CPU
Intel(R) Core(TM) i7-860 @ 2.80GHz
Motherboard
Gigabyte Technology Co., Ltd. P55-UD3L
Memory
4.00 GB
Graphics Card(s)
NVIDIA GeForce GTX 750
Sound Card
(1) Line 6 UX2 (2) Realtek High Definition Audio
Monitor(s) Displays
23" acer
Screen Resolution
1920 x 1080 x 32 bits (4294967296 colors) @ 60 Hz
Hard Drives
(1) WDC WD5000AAKS-00D2B0 ATA Device (2) Seagate FreeAgent Go 250G USB Device
Cooling
Corsair H75 liquid cooler (Very easy to install, actually)
Internet Speed
60M cable modem-->Linksys E1200-->1Gbps net card
Browser
Chrome
Other Info
This is probably the longest I've ever had a Windows machine run without having to restore it to scratch. I'm used to restoring to "factory" about every 2 yrs. I've run with Win7 since new in 2009 and only recently (Nov, '14) restored to clean up the machine from all my 'xperimenting. LOL!! I may never need another machine.
Upgraded to 10 when it was still free, then installed 2017 update.