Wolfgang Kandek, CTO of security firm Qualys, learned the hard way that reusing passwords can backfire. Kandek says, "I used to use a common 'beater' password for these types of sites, but it recently came back to haunt me when my password at Stratfor leaked and in the subsequent inventory I found that I had used it for many sites that I have come to consider important."
Kevin Haley, director of Symantec Security Response, warns that zombie accounts could get hacked, and that the data shared with those accounts could be stolen or exposed--but he also notes that the risk isn't necessarily any greater than it is for the sites you actively use.
Keep in mind, however, that more-obscure sites and services don't have the resources of Facebook or Google, and may not be as actively maintained and protected.
Deactivate or delete unused accounts and applications
If you're not going to use a social network, app, or online service any longer, shut down your account. In many cases people simply walk away and stop using a tool or service, but leave it active and do nothing to remove or protect any information it has access to.
Many sites and services don't have a defined data-retention policy, so as far as you know the data you posted to your account could be retained indefinitely. A server breach or compromise years from now could expose information that you forgot you ever even shared.
Paul Henry, security and forensic analyst for security firm Lumension, cautions that deactivating an account and removing sensitive data is easier said than done. "Look at sites like Facebook--you really have to work to remove your data. Even if you delete your information, it will still be around for at least 30 days. And if you then log back in within that 30-day window, they'll keep your information forever, even if you redelete."
Henry also stresses that unused applications and plug-ins are a bigger threat than the possibility of a forgotten website being hacked. Odds are good that you aren't patching and updating software you aren't even using. When attackers find vulnerabilities in those programs, they become an easy back door for compromising your PC.