BAGHDAD — The extremist group battling the Iraqi government, the Islamic State in Iraq and Syria, may practice a seventh-century version of fundamentalist Islam, but it has demonstrated modern sophistication when it comes to using social media, particularly Twitter and other sites like WordPress and Tumblr.

On Twitter, ISIS has hijacked World Cup hashtags, flooding unsuspecting soccer fans with its propaganda screeds. It has used Facebook as a death-threat generator; the text-sharing app

JustPaste to upload book-length tirades; the app SoundCloud for jihadi music; and YouTube and Twitter for videos to terrify its enemies.

One Twitter account that purports to be linked to ISIS even altered a picture of Michelle Obama to boast about its capture of American-made war matériel. The sign in her hands was changed from one saying “#BringBackOurGirls,” referring to the worldwide campaign to save the schoolgirls abducted in Nigeria, to one saying “#BringBackOurHumvee.”

ISIS has outfought both its Syrian rivals and the Iraqi government online, as well as on the battlefield. The Iraqi government’s response has been to order Internet providers in the country to block most social media sites.