The titular phrase (usually just "OTM") refers to border crossers who come from countries other than Mexico. About 60,000 OTMs were detained after crossing the border last year. Some were originally from countries like North Korea, Iraq, and Libya. While most might be "good-hearted people who are coming here to work", certainly there are some who are not.

And, unlike Mexican illegal aliens, a large number of OTMs are released into the U.S. and are never found again.

The report "Officials: OTMs 'a very grave problem'" describes how many such OTMs cross in Texas because they know that due to the lack of detention space they'll be given orders to appear in court and then sent on their way. And, many of these OTMs are more or less giving themselves up, because news of the lack of detention space has been covered in the sending countries.

For background on this issue, see the following:
"Illegals detained at border released onto U.S. streets"
"[Rep.] Bonilla demands review of OTM release policy"
"Illegals from terrorist nations are crossing the border into Arizona"
"Rep Ortiz: Non-Mexican migrants getting free pass into U.S."
"Border Patrol Releases Immigrants at Bus Station" ("Action 4 News undercover cameras catch Border Patrol agents dropping off illegal immigrants at a local bus station [in Harlingen, TX] by the van load.")
"Unholy Border Alliance"
"Fun facts about Fort Huachuca" (not specifically about OTMs, but the fact that 3,000 illegal aliens have been caught on a military base should be worrisome)
"Other Than Mexicans" (Tuscon Weekly article has a roundup of several terrorism-related OTM incidents)
"U.S. Fears Terrorism Via Mexico's Time-Tested Smuggling Routes"

Chapter 3 of the 9/11 Commission Staff Report included the following:

...Thus, abuse of the immigration system and a lack of interior immigration enforcement [prior to 9/11 attack] were unwittingly working together to support terrorist activity...

...there are uncorroborated law enforcement reports suggesting that associates of al Qaeda used smugglers in Latin America to travel through the region in 2002 before traveling onward to the United States...

...One smuggler, Salim Boughader-Mucharrafille, smuggled Lebanese nationals sympathetic to Hamas and Hizbollah into the United States and relied on corrupt Mexican officials in Beirut, Mexico City and Tijuana to facilitate their travel...