Online jobs firm Monster Worldwide has acquired SF-based Affinity Labs, a developer of community sites centered around various vocations, for $61 million in cash. Examples of its portfolio include Policelink.com, NursingLink.com and ArtBistro, each of which offers community, social networking and content related to the stated vertical. Affinity Labs was founded by CEO Christopher Michel, who previously founded community and social networking site Military.com, which was also sold to Monster in 2004. Michel will now join Monster management. Already, Monster and Affinity had a strategic relationship, whereby Monster sold advertising for the company, while Monster users had direct access to Affinity’s services. Affinity, which has backing from Mayfield and Trinity Ventures, raised less than $10 million in a first round last year according to VentureWire. Release.

The idea behind the acquisition is pretty clear: it’s a bet that social networking will grow in importance as part of the career search process. Social networking sites, particularly LinkedIn, but others as well, are seen as growing competitors to the established jobs sites. So now Monster is getting more aggressive about pushing back.

• Military Portal Bought By Monster