JKapDRC wrote:
And also, should I install a (free) malware/anti-virus scanner? If so, which one?
You've been infected by what appears to be the latest strain of the Flashback Trojan Horse, although the question is not settled yet. See this thread
<https://discussions.apple.com/thread/3844172>
which seems to have been the first mention of this strain. In addition to <~/.rserv>, you probably also have <~/Library/LaunchAgents/com.adobe.reader.plist>, which is the launch agent periodically running .rserv.
Regarding clean-up, so far, none of the A/V people seem to have picked up on it, so installing any A/V utility at this point may not do you any good. Until they are updated to deal with this strain, you cannot be sure that they will detect it or clean it properly. WRT Flashback, I would not trust any A/V utility. IMHO, the only safe solution is, as recommended by Linc Davis, to erase the hard disk and re-install from backup—if you have a backup which you are absolutely sure pre-dates the date of infection. Otherwise, I'd install the OS anew, re-install from the original installers, and restore from backup documents only; no apps and no preferences or configuration files.
Further, any password used since the infection must be considered compromised, and that could be your bank account, Gmail, or this forum. As soon as you've cleared the infection, go immediately to any account you've accessed (this forum included) and change the password.
As precautionary measure, disable Java in all your browsers, not just Safari; and consider whether or not un-installing it altogether might not be a bad idea.
There are a few additional things which you might be interested in doing before erasing everything (disconnect from the network while doing it).
Take .rserv and com.adobe.reader.plist (it has nothing to do with Adobe Reader, btw), zip 'em together, and save the archive to submit it to A/V sites, like ClamAV or VirusTotal.
Check you browser history and log messages (in Console). See how trungson did it here
<https://discussions.apple.com/thread/3844172?answerId=18010355022#18010355022>
It might give you an idea of when the infection occurred. The primary vector seems to be hacked or infected Wordpress blogs, but no-one seems to know for sure if there are others. That's why I asked what message board you were on—it would be useful to check what software it's running on and if it has been hacked.