atlrus - 3:12 pm on Aug 21, 2013 (gmt 0)
And can I expect a penalty on my site (the site is currently doing very well and no sign of that at all)?
These guys are doing you a favor. Google will not send unnatural links warning for just one link, chances are those 10 websites have rather shady link profiles, so linking to them is not beneficial to you at all.
I am personally advocating against using "nofollow" in any and all cases.
No one really knows the full extend of the attribute, among other things Google is advising to be used on paid links and you don't want your website to be associated in any way with paid links, advertorials, etc. If you still want to link out to such websites - just use a redirect script through a folder in your website and ban search engines access to that folder.