If you’ve ever had the distinct misfortune of opening a spam message and accidentally downloading a virus to your computer, you know how frustrating it can be to watch as you slowly lose control of your computer to malware. Of course, those were the old days. Now, when you download a virus, you don’t just feel the shame of losing your own computer, you have to deal with the guilt of potentially infecting all of your friends on Facebook and Twitter too.

For as much as we love how social networking sites bring us together, cybercriminals love them even more. Thanks to the sheer size of many social networks, it is very difficult to institute strong security policies. Because of this, it’s never been easier for spammers and hackers to spread worms and other malicious programs into the site before anyone can diagnose and rectify the problem. Even worse, when these worms spread, it not only hurts your friends, but it ruins your reputation in the process.

A recent article for the New York Times further explores this problem.

Malicious programs are rampaging through Web sites like Facebook andTwitter, spreading themselves by taking over people’s accounts and sending out messages to all of their friends and followers. The result is that people are inadvertently telling their co-workers and loved ones how to raise their I.Q.’s or make money instantly, or urging them to watch an awesome new video in which they star.

“I wonder what people are thinking of me right now?” said Matt Marquess, an employee at a public relations firm in San Francisco whose Twitter account was recently hijacked, showering his followers with messages that appeared to offer a $500 gift card to Victoria’s Secret.

Mr. Marquess was clueless about the offers until a professional acquaintance asked him about them via e-mail. Confused, he logged in to his account and noticed he had been promoting lingerie for five days.

“No one had said anything to me,” he said. “I thought, how long have I been Twittering about underwear?”

The humiliation sown by these attacks is just collateral damage. In most cases, the perpetrators are hoping to profit from the referral fees they get for directing people to sketchy e-commerce sites.

In other words, even the crooks are on social networks now — because millions of tightly connected potential victims are just waiting for them there.

The article goes on to compare the good old days when viruses only spread through e-mail.

Earlier malicious programs could also cause a similar measure of embarrassment if they spread themselves through a person’s e-mail address book.

But those messages, traveling from computer to computer, were more likely to be stopped by antivirus or firewall software. On the Web, such measures offer little protection. (Although they are popularly referred to as viruses or worms, the new forms of Web-based malicious programs do not technically fall into those categories, as they are not self-contained programs.)

Getting tangled up in a virus on a social network is also more painfully, and instantaneously, public. “Once it’s delivered to everyone in three seconds, the cat is out of the bag,” said Chet Wisniewski of Sophos, a Web security firm. “When people got viruses on their computers, or fell for scams at home, they were generally the only ones that knew about it and they cleaned it up themselves. It wasn’t broadcast to the whole world.”

Everyone makes mistakes, and if you’ve accidentally sent your whole social network a malicious worm, you should try your best not to feel too bad about it. Still, it would be hard to stomach the embarrassment. The only way to really save yourself the embarrassment of spreading a virus is to make sure you don’t click on anything that seems suspicious. If you get a weird message that appears to be from a friend, don’t open it without confirming its authenticity with them first. The odds are good that if it is a spam message, they don’t even know about it yet. If you do click on a spam link, however, you should do your best to notify your friends and family and work with the social network to shut down your account temporarily.