I used to like to read and participate in some of the LinkedIn groups about design and human factors but lately it just all looks like "make money fast" schemes and diploma mills. Somebody sets up an account and joins about 50 groups and the spams every group with the same message once a month with a link to website that just screams Virus Central. If you look at the account there's never any information about the user and they have no Connections. Some group owners are good about kicking the spammers out, and other group owners don't seem to care.
In some cases, I think the spammers are just clueless individuals who read a poorly-written article about social media and have implementated the first idea that came into their heads.