PSA: If you are not browsing the interwebs with a VPN enabled and you suddenly find your browser sessions are frequently stymied by constant CAPTCHA requests, that's one potential sign that your system may be compromised by something that is routing other peoples' Web traffic through your computer. It's not a dead giveaway of a compromise by any stretch, but it is something that you should probably investigate further.
Upon further consideration, I feel should point out that many low-cost or "free" VPNs very much do route other peoples' traffic through your system. This is an incredibly common practice among "free" or low-cost VPN providers. Just understand that running a VPN is not cheap, and anyone giving it away for free probably does not have your best interests at heart.
@briankrebs As a tip, if you use LinkedIn, your privacy will be compromised. ;-)