I have been getting the same since 10am UK time on Wednesday, and the IP addresses trying to gain access have been in Thailand and Ukraine amongst others.
It would be nice to hear from the Moderators what suggested actions we should take.
I have already changed my password to one that is very unlikely to be cracked by brute force.
I don't believe in co-incidences, and the timing along with Heartbleed is intriguing.
Heartbleed?.......... no way.
Ignore them is what you do. This has happened on all forum software since the 'net began.
I have had this at both VB sites several times a year for the last 7 years, and on every forum I have membership of.
It is called a BOT. Never heard of XRumer?
Just make sure you have a decent password that the Bot can't break.
Surely as forum admins you should know what is happening?