The Google Webmaster Blog on Blogspot has a great definition of what user profile spam is and should be read by all SEO professionals which is entitled Spam2.0: Fake user accounts and spam profiles
Welcome to the world of spam profiles. The social web is growing incredibly quickly and spammers look at every kind of user content on the web as an opportunity for traffic. I've spoken with a number of experienced webmasters who were surprised to find out this was even a problem, so I thought I would talk a little bit about spam profiles and what you might do to find and clean them out of your site.
Why is this important?
Imagine the following scenario:
"Hello there, welcome to our new web2.0 social networking site. Boy, have I got a new friend for you. His name is Mr. BuyMaleEnhancementRingtonesNow, and he'd love for you to check out his profile. He's a NaN-year-old from Pharmadelphia, PA and you can check out his exciting home page at http://example.com/obviousflimflam.
Not interested? Then let me introduce you to my dear friend PrettyGirlsWebCam1234, she says she's an old college friend of yours and has exciting photos and videos you might want to see."
You probably don't want your visitors' first impression of your site to include inappropriate images or bogus business offers. You definitely don't want your users hounded by fake invites to the point where they stop visiting altogether. If your site becomes filled with spammy content and links to bad parts of the web, search engines may lose trust in your otherwise fine site.
Why would anyone create spam profiles?
Spammers create fake profiles for a number of nefarious purposes. Sometimes they're just a way to reach users internally on a social networking site. This is somewhat similar to the way email spam works - the point is to send your users messages or friend invites and trick them into following a link, making a purchase, or downloading malware by sending a fake or low-quality proposition.
Spammers are also using spam profiles as yet another avenue to generate webspam on otherwise good domains. They scour the web for opportunities to get their links, redirects, and malware to users. They use your site because it's no cost to them and they hope to piggyback off your good reputation.
The latter case is becoming more and more common. Some fake profiles are obvious, using popular pharmaceuticals as the profile name, for example; but we've noticed an increase in savvier spammers that try to use real names and realistic data to sneak in their bad links. To make sure their newly-minted gibberish profile shows up in searches they will also generate links on hacked sites, comment spam, and yes, other spam profiles. This results in a lot of bad content on your domain, unwanted incoming links from spam sites, and annoyed users.
Which sites are being abused?
You may be thinking to yourself, "But my site isn't a huge social networking juggernaut; surely I don't need to worry." Unfortunately, we see spam profiles on everything from the largest social networking sites to the smallest forums and bulletin boards. Many popular bulletin boards and content management systems (CMS) such as vBulletin, phpBB, Moodle, Joomla, etc. generate member pages for every user that creates an account. In general CMSs are great because they make it easy for you to deploy content and interactive features to your site, but auto-generated pages can be abused if you're not aware.
For all of you out there who do work for huge social networking juggernauts, your site is a target as well. Spammers want access to your large userbase, hoping that users on social sites will be more trusting of incoming friend requests, leading to larger success rates.
What can you do?
This isn't an easy problem to solve - the bad guys are attacking a wide range of sites and seem to be able to adapt their scripts to get around countermeasures. Google is constantly under attack by spammers trying to create fake accounts and generate spam profiles on our sites, and despite all of our efforts some have managed to slip through. Here are some things you can do to make their lives more difficult and keep your site clean and useful:
Make sure you have standard security features in place, including CAPTCHAs, to make it harder for spammers to create accounts en masse. Watch out for unlikely behavior - thousands of new user accounts created from the same IP address, new users sending out thousands of friend requests, etc. There is no simple solution to this problem, but often some simple checks will catch most of the worst spam.
Use a blacklist to prevent repetitive spamming attempts. We often see large numbers of fake profiles on one innocent site all linking to the same domain, so once you find one, you should make it simple to remove all of them.
Consider nofollowing the links on untrusted user profile pages. This makes your site less attractive to anyone trying to pass PageRank from your site to their spammy site. Spammers seem to go after the low-hanging fruit, so even just nofollowing new profiles with few signals of trustworthiness will go a long way toward mitigating the problem. On the flip side, you could also consider manually or automatically lifting the nofollow attribute on links created by community members that are likely more trustworthy, such as those who have contributed substantive content over time.
Consider noindexing profile pages for new, not yet trustworthy users. You may even want to make initial profile pages completely private, especially if the bulk of the content on your site is in blogs, forums, or other types of pages.
Add a "report spam" feature to user profiles and friend invitations. Let your users help you solve the problem - they care about your community and are annoyed by spam too.
Monitor your site for spammy pages. One of the best tools for this is Google Alerts - set up a site: query along with commercial or adult keywords that you wouldn't expect to see on your site. This is also a great tool to help detect hacked pages. You can also check 'Keywords' data in Webmaster Tools for strange, volatile vocabulary.
Watch for spikes in traffic from suspicious queries. It's always great to see the line on your pageviews chart head upward, but pay attention to commercial or adult queries that don't fit your site's content. In cases like this where a spammer has abused your site, that traffic will provide little if any benefit while introducing users to your site as "the place that redirected me to that virus.